I feel like the only reason sorcerer don't have True Polymorph is because of twin spell. It easily breaks the spell(then again, balance has already gone out the window by 17th level). Imagine the sorcerer turning 2 people into dragons. As for Shapechange, other than MAYBE extended spell, I don't see any real reason why they don't have it.

Quote from Lyxen >>

Quote from Pompo >>

The problem in my personal experience is that Sorcerers are not weaker, just less fun to play. They still get all the big damage spells which bring them in line with other classes damage-wise but get no rituals and limited utility spells. I have a hard time seeing myself ever playing one outside of a combat-focused one-shot. True Poly is a perfect example, instead of the fun and creative spell that allows them to do fun stuff AND be good in combat, Sorcerers get Power word: Kill, Meteor Swarm, Psychic Scream, and other more damage focused spells. Then to top it off they get the less fun combat oriented version of the spell: Mass Polymorph. This pattern is then repeated throughout their spell list. I would have no problem with this in a videogame or some other more combat-focused tabletop game, but in DnD it just leaves a bad taste in my mouth.

Then again, It's easily fixable by giving them rituals, a slightly expanded spell list, and giving old subclasses the expanded spells treatment from Tasha, but I get that homebrew is never the ideal solution

 
The thing is that most people do not really understand the difference between Sorcerer and Wizard at more than a cosmetic level, because they see basically the same spells. But from its inception, the Sorcerer has bean made to be a simple damage dealer for the people who wanted arcane magic and not too much preparation and maintenance work (because managing a wizard's spellbook and his daily spells is quite a bit of work). So it's an efficient damage dealer, and is not made to be versatile at all. Actually, this is probably the main reason for restricting the spell list in 5e. Seeing that, in general, 5e spells are  more versatile, it compensates.

My perspective is that, indeed, it is more limited than the wizard, who is actually much better played as support/controller because of the huge versatility of choosing the right spell for the right situation. Whether you find that blaster role fun or not depends on you, if you don't want to play a sorcerer, play a wizard, but lots of people in my groups who are more damage oriented really like the sorcerer.

 Yet you like the Shadow sorcerer with Subtle Spell, and Clockwork Magic and Divine Magic aren't blaster lists at all...

I would theorise that a True Polymorph wizard could convert creatures "At Will" spell slots into sorcery points infinetly.

You don't retain any of your class features while you are True Polymorphed so they couldn't do that.

Consider the following twined true polymorph.

I literally had this character - a Dragonborn Sorcerer who aspired to be a real Dragon. He managed this, eventually, with a Wish spell. There was a degree of DM approval needed - we both agreed it fit the narrative arc of the character. However, it was also agreed that the character was ‘retired’ as a PC after he had transformed. It was a permanent transformation. 

Given the nerfs to Twinned Spell in the playtests, it would be great if Sorcerers could now access spells like True Polymorph, Shapechange, and other exciting options in the new edition.

Quote from Lanir >>

Given the nerfs to Twinned Spell in the playtests, it would be great if Sorcerers could now access spells like True Polymorph, Shapechange, and other exciting options in the new edition.

 nah im betting they will get nerfed again