I recommend having a similar but different homebrew option for NPC's and sidekicks than is currently presented in when creating NPC's in the monster homebrew section. These NPC's could be made how monsters are currently made but would also have specific NPC options meant to be quick and simple. This avenue would also have easily selectable options for sidekicks as described in Tasha's Cauldron of Everything where the DM can select from option similar to character creation. Another important part of this would be the option to add them to your campaign so when the DM creates encounters, they can include friendly NPCs and sidekicks in DnDBeyond's encounter builder without the NPCs counting against the encounters budget when determining difficulty.

I have been trying to build NPC's using character stats and feats, and it is for all intents and purposes impossible do this quickly and easily. If i build them in the character builder, they are not easily integrated into my Campaign.  And If I build them in the Homebrew Monster builder, there is no option to build anything but Monsters. I WANT NPC's that are like traditional PC's from the Players Handbook not like Dragons and Zombies :/    

The designers of 5e intended for all NPCs to be made using monster statblocks, not to be built the same way as PCs. Characters built as PCs have several shortcomings when it comes to using them as NPCs. For one thing they’re chock full of useless information that a DM has to flip through. That stuff is useful for a PC, but usually just gets in a DM’s way, especially during combat. Another shortcoming is that PCs are designed to be glass cannons compared to monsters. They dish out a ton of damage, but go down relatively quickly too. That’s to make players feel like mighty heroes, but also make your palms sweat a little when the HP start to run low. By comparison, a monster built NPC does a more measured amount of damage but can stay standing long enough to make combat entertaining to the players. A third major shortcoming is that a PC built character has a very limited action economy, whereas a monster built NPC can have whatever action economy it needs to in order to present an appropriate challenge to the party. If an enemy NPC requires the DM to spend 10 minutes to take its turn, deals too much damage all at once, can’t spread things around to threaten the whole party, and goes down too quickly it just makes players feel less enthusiastic about combat.

What I usually do is to find a monster statblock that has a similar flavor as what I want and augment it. For example, if I want a “holy man” monk who’s an orc and has a tiny bit of divine spellcasting, I don’t build that as a PC. I take the martial arts adept (or the Legacy martial arts adept), apply the orc racial traits and ASIs, add an appropriate background and give it a feat and viola, I end up with this: (https://www.dndbeyond.com/monsters/2867450-ogrul-kharag-martial-arts-adept). The background offers me quick select personality characteristics to even flesh them out with as you can see from that example. Now, that’s one I’ve polished up for publication here on DDB, but I can slap together a quick and dirty version in as little as 5 minutes if I need to. I’ve even published several other examples you’re welcome to use too.

Now, for very, very special NPCs I do make them as PCs, but then I convert them into monsters before actually using them. I start with a simple class & subclass, strip out the bloat, often shave off some damage, usually boost their action economy, and then definitely double their hit dice (and therefore their HP). That turns a PC built NPC like this: (https://www.dndbeyond.com/characters/96595795), into an easier to use and better balanced NPC like this: (https://www.dndbeyond.com/monsters/3945608-sir-reynglian-trueanvil-20th-level-npc). But as you’ve noted, that takes time, a lot of time. That’s why I save this method for BBEs and the like. Their notable underlinings I usually (but not always) do the other, easier, faster way. Regular mooks just get regular off the rack statblocks unless and until they become noteworthy enough to get customized at all.

my mind is muddled from that insanely long post

You should see some from another user I know. *woofta* She runs long.

D&D Beyond just really needs to incorporate a Sidekick creator (based on the Sidekick rules from Tasha's) so that they can be easily created and leveled up as the party goes. This would solve a lot of issues that others have noted when trying to use a full PC build as a sidekick/NPC. It reduces the amount of bloat of details and abilities while still allowing you to easily change them as the party levels up.

I really want to use this for a counter-group of adventurers I have that serves as a semi-antagonist to the main party, however there isn't an easy way to do this in D&D Beyond currently, and having to manually alter a homebrew Monster when the group levels up is exceptionally tedious.

Come on, D&D Beyond devs! I'm pretty sure this has been on the "to-do" list for a long time. Please?