I dont know if this is in the wrong area, but it does say "feedback" so here i go.

Ive tried getting into 5th edition but any improvements to lesser used options I see are small with huge trade backs. Everything I can think of liking or working towards has been cut out. I think this is meant to be GM friendly as they dont have to question if one of the 30+ classes, skills, feats, items are actually in the game.

#1 Extra Attacks are class and level based. Some classes never gain Extra attacks. THAC0 and BAB were not the best systems but they worked well enough to make multiclassing a viable option as well as various ways to increase your chance to hit and get additional attacks with any attack instead of a Monk only getting extra unarmed hits.. Fighter has the dubious distinction of technically being the only character to have 4 regular attacks without some crippling specialization, and even that comes after 20 levels .

#2 Ability Scores and Feats. Now in 5th edition you cant get both as every improvement means a Feat lost and vice versa. Unpleasant GMs wont even allow Feats as they are technically Optional Rules.

#3 Spells and Concentration. Spells no longer scale to caster level making them specialized and eventually obsolete. The number of higher tier spells per day is highly reduced until its only 1 per day at tiers 8-9. There are no bonus spells for having a high aptitude in your caster stat. Spellcasters dont have much to do, unless you picked a Warlock.

Concentration is a new major drawback as most spellcasters have to take the Resilience feat to be able to Concentrate with any reasonable amount of success.

#4 Skills and SKill Proficiency. Characters dont gain skill points to place them wherever their character is focused on. Instead they gain skill Proficiency that are limited by class and character background. Only having a background as a Pirate means good eyesight and hearing for example.

#5 Multiclassing, there are conflicting problems preventing classes from stacking anything like extra attacks, more spells than a single class caster, and proficiencies being limited. Seems like its trying to force people to be the core classes at the expense of freedom.

#6 Magic items. Attunement is a conflict with finding rare and powerful magic items but at the same time you cant use what you find. There is effectively a magic item per character cap, much smaller than any other game I have ever played. Go through hard quests and sorry you cant reward is junk.

#7 Resting and abilities. In general it means your party has to take breaks frequently with some character classes being shown favoritism by getting abilities back after short rests and others after long rests.

as someone who started "back in the day", i loved Thac0. However, i spent the majority of my time in 3 and 3.5.

While i can see your points, these actually need to be addressed by Wizards of the Coast. DNDBeyond is owned by Twitch, an Amazon company and only has a licensing agreement with WoTC. They don't really get to input on how the game is designed/created.

I'm reading this as an "older" player who started with 3/3.5E? As someone who started with the basic box sets and progressed through 1E and 2E, I see 5E as the only modern edition of the game that i can even play. It offers a ridiculous amount of options and customization to players (IMO) but keeps the crunch to a level I can actually handle as a DM. I skipped 3E & Pathfinder completely - looking at it just makes my brain hurt. I can't imagine keeping all that straight as a player let alone as a DM.

It sounds like you preferred that level of rules crunch, optimization an so on, which is great. It just may be that 5E isn't for you. There is certainly no reason to switch if that is the case, or maybe switch to PF? In any case, as Cee noted, your feedback is really for Wizards, not the Beyond staff. This site is merely a digital source for the rules as published by WotC. Unless of course you're just looking for conversation on the merits of 3E vs. 5E. It's always a possibility you can find that here on the forums. It may even stay civil and not degenerate into an edition war, who knows?

So as someone who heavily played in 3.5E and not runs 5E I have run into many things I felt as "different".

I don't think 5E is trying to take away options but to make the game more streamlined. I never DM'ed for 3.5e but the options were crazy for players to have, now as a DM for 5e, I couldn't imagine running a 3.5e campaign, it's a ridiculous amount to keep track of.

My favorite and probably one of the most controversial things is Attacks of Opportunity which I believe to be way nicer in 5e. Are they as real as 3.5e, no but it makes the combat seem so much more streamlined and easier to manage.

I do think 3.5e has a lot more depth and what feels like more customization, but I also feel as though 5e feels like a good balance between depth, customization, and simplicity.

As a player who has been playing since the early days of D&D, I have played and DM every edition.  Each edition had their good points and bad points.  Personally, I like 5e just from a simplicity stand point.  OD&D, AD&D were extremely constrained when it came to player options.  Your selection of class was limited by ability scores and in some cases race.  Some races were limited to what level they maxed out at.  There were only a few multi-class options and don't get me started on THAC0.  Second edition began expanding on classes.  This was further expanded on by 3/3.5e.  It was at this point where video games started to have an influence on RPGs. 4e was very influenced this way.  Which is the problem.

Like it or not, many people who speak of DPS or DPR or optimizing, especially with multi-classing, are video gamers that like D&D. As a general rule this clashes with what an RPG is at its core. it is a Role Playing Game, emphasis on Role, like a part in a play.  If you watch, Critical Role or Dice, Camera, Action or the other dozens of streaming game play you will notice that combat is less than half of what is done in any given session.  In fact, I have run sessions that had no combat at all.  For the most part, a combat optimized character is mostly useless in many campaigns, mine included. I have also run dungeon delves where such characters would be perfect, these are just hack & slash or endurance campaigns. So just something to think about.  To answer your questions:

#1: in the earliest version of D&D, only melee attacks would increase, specifically fighters and Monks, then Paladin, rogue, cleric, druid, and Magic-user.  The number of attacks was pretty convoluted.  You would go 1/1, 3/2, 2/1, 3/1, 4/1 and fighters at like 18th got 5/1. As you can see that is pretty much a pain. The number of attacks was most important to the fighters , monks and rogues.  The cleric, druid and magic-user would max at either the 3/2 or 2/1. The monk and Paladin topped out at 4/1. These attack only applied to melee weapon attacks.  Spells were 1 per round unless it stated longer and some spells required concentration during the entire duration. For me, this is not a big deal, not every class could get multiple attacks back then as it does now.

#2: Feats didn't really exist until 2nd edition, you pretty much just role played your attacks, in AD&D feats were just flavor for the most part. As many feats are optional just because a DM doesn't allow them doesn't make them mean, they just don't want to deal with them.  Ability score improvement with level came about mostly in 3/3.5e.  In older editions ability scores could be improved during down time by training, learning or some other activity and would take x amount of gp and x amount of time to usually a year to gain 1 point in 1 ability score. Ability scores were capped based on race and could only be raised above that by magical means.  Your ability score were also affected by the age of your character, which meant the older your character got, their strength, constitution and dexterity would permanently go down.  that was done away with in 3/3.5e.

#3. Spell never used to scale with the caster, the spell level in AD&D was pretty much set in stone and didn't change.  They might have scaled in 3/3.5 but I am not sure.  Some spells do scale as you can cast a spell at a higher level. Though in the older editions you did get extra spell slots for high intelligence for magic-users and high wisdom for clerics, druids and paladins.  As for the few number level 8 and 9 spells, that has always been that way as far as I know.  As best as I can remember spells scaling with level is more of a video game mechanic than D&D mechanic.  It really isn't an issue since those higher level spells are pretty powerful. As I stated earlier, concentration has been around since AD&D and was the weakness of spell casters besides hit points.

#4:Skills and skill proficiencies are a recent addition, really starting with 3/3.5e.  In earlier editions the only skills or proficiencies were languages and thief skills.  Other than that if you could convince the DM your character could do something you did it, if not than you didn't.  2e did have some skills in it, but skills were optional.  The skills in 5e are pretty good overall.  You are not-proficient, proficient or an expert in a skill. Anything not covered in the list is an ability check.  This hearkens from AD&D.  You actually have more freedom with this system as you can role play the skills fairly broadly and you aren't trapped into a specific skill set.  You can still attempt the other skills and even those that aren't listed by using ability score modifiers.

#5: multi-classing has been around since AD&D, back then you had to choose from a list of multi-classes and some classes couldn't multi-class. As for leveling, it is about the same as it was back in AD&D, If you had a dual class character level 15 was your max, thee class character level 10 was your max.  The cons generally outweighed the benefits in that system.  they were still fun to play, but lagged once you hit the max level.  AD&D allowed you to level up beyond 20th level.  I had 1 character that survived to what was essentially 60th level before I retired him.  Mostly from what I have scene in forums on multi-classing, the goal is combat power.  Which for many gaming session combat is 25% of the session, in some it is 10% or less.  These characters are rarely about role playing and all about kill! Kill! Kill!  In my campaigns those types of characters rarely shine unless I am running a dungeon delve, hack & slash or endurance campaign.  I have nothing against multi-classing as long as it fits with the world you are playing.  As a rule outside of those three campaigns I rarely allow a starting character to multi-class, and if one does multi-class it has to be plausible as to how and why they are learning this class. The main reason they don't allow the stacking in 5e is really because of what happened with 3.5 and 4e, you started to get god like characters that could almost fell a dragon in a single attack. It is also to limit the optimizing of characters solely for combat. 5e is an attempt to go back to the role playing roots rather than the number crunching combat centric style of of 3.5 and 4e.  Role-playing is the core of D&D, the combat is just the flavoring.  Optimizing and   Multi-classing for the most part is a video game aspect that people bring over to the table top game solely for the purpose of buffing attacks.

#6: I am not sure you fully understand how the magic items works.  There are some magic items that require attunement, and these are restricted 3.  There are also many different magic items that do not require attunement and you can have as many of these as your DM allows.  There are suggested limits on the number of magic items a character can have per tier, but this is by no means a requirement.  Personally, I have no problem restricting the number of magic items.  From your statement I gather you are looking at this from a modifier stand point in which case you are looking at the optimization and combat power aspect.  This a change that really only bothers people who only look at DPS/DPR.  There is more to D&D than combat.  This is another idea that stems from video games, I play Neverwinter and have a crap ton of magic items, most of which I couldn't have in the table top version.  This really isn't an issue unless you only care about combat, in which case it would be up to your DM.

#7: the rules for resting in 5e are more liberal than in some of the older editions.  With AD&D you had long rest, which couldn't be interrupted or you had to start over. In 5e each class has gains that can be made from a short rest and gains from a long rest. Depending on the campaign resting can have a negative impact on the end results since time matters in D&D. Most video games allow you to rest whenever you want for how long you want with few if any repercussions.  I have been in and run campaigns that time is as much the enemy as the bad guys.  Excessive delays could have cataclysmic consequences. In this regard 5e makes you think about what you are doing.  Should you cast that spell now or later.  Should you attack that group of goblins or go around.  This goes back to what I mentioned earlier 5e went back to D&D's role playing roots where role playing is 75% or more of a session rather than combat being a majority of a session.

Most of what you are finding negative about 5e stems from a mindset that is based on video games or 3.5. This is neither bad or good. You are looking at it from a pure power and survivability point of view which is derived from many first and third person shooter games and MMOs.  Depending on your gaming group this will be good or bad.  Many of the restrictions you are mentioning exist for balancing reasons, so that no single class is much more powerful than any other class.  As I have seen in many different forums, this doesn't stop people from optimizing and coming up with way to boost combat power. The problem is 5e is not combat centric, so these types of characters are not as good outside of combat. Many of the restrictions you mention are easily remedied with character management.  You know numbers, it is up to you to manage your characters actions.  Every encounter doesn't have to start or end in combat.  If a party manages their actions properly, they can do a lot without ever fighting.  Overall, I think has more to do with your play style and preference.  Truthfully, there are hundreds of role-playing games out that might be better suited to what you want. If you want to get away from the MMO, video game grinding style of play for something more role-play and story oriented than 5e is the way to go.