I honestly find it hard to believe that anybody is seriously griping about this.
Why is it so hard to believe? In previous editions sorcerers had clear unique advantages from first level, along with unique limits and restrictions. 5e has the clear limits and restrictions from level 1 -which are harsher than ever- but they have no clear payoff until very high levels, Is it so wrong to want more uniqueness from day 1?
The sorcerer's uniqueness lies in being able to dominate multiple creatures at once (twin spell)
A possibly overpowered combo doesn't necessarily make a class worthy. More so if it means losing out on many useful spells because they could be overpowered if twinned.(And if those same overpowered combos could be pulled out by a multiclassed bard or wizard who poached twin spell via multiclassing)
granting themselves advantage on any spell with an attack roll (quicken spell + true strike cantrip; or wild magic),
Yes, it can be useful -and something to love-, but it is costly, and wild magic is very unreliable and dangerous. You are better off with Lucky.
casting spells while disguised as an orcish grunt without anyone realizing it (subtle spell),
Another lovely thing, but it is easily poachable by a short dip. And I don't know you, but third level is too high. What about the first two levels? don't we deserve to feel sorcerous at low level too? Subtle spell -or at least no material components- should be something all sorcerers can do for free.
using offense magic while simultaneously protecting one's self from weapon attacks (quicken spell + dodge or blade ward),
Again, it is costly. And you need to wait for third level.
straight out bypassing magic resistance (heighten spell), etc...things that no other class can accomplish.
Again, for most of your career as sorcerer you can only do two things out of all of those,(just like the bard, warlock or wizard dipping to get them, and they have all of those extra unique spells) And so far your examples are limited on how to make a given spell better, but not necessarily replace the need for more spells, without things like admixture and energy substitution metamagic barely justifies the class having so few spells, both at any time and in general.