And I agree. But how often a metamagic or a pact feature has been key to success compared to the versatility the wizards enjoy? Versatility is always "on". Whereas the features of the warlock and sorcerer can be situationnal.
For the sorcerer, I see more spell slots created or quickened spells than anything else.
For the warlock, EB spamming is just about it. He can't even take the SS feat with his spells. So a SS will always be better than him. Of course repelling blast can be a nuisance for some monsters but otherwise, the wizard can do everything the warlock does.
IME, metamagic and invocations are
HUGE and offer enormous benefits to those classes. Nothing says loving like dropping darkness on a foe and having advantage to hit him with EB and he has disadvantage to hit
you at the same time. And the Shadow Magic Sorcerer who creates darkness with spell points can
also see into it, gaining the advantage on his attacks as well; and it frees the Warlock to concentrate on Hex.
Arguably, there are only a handful of invocations I think are really awesome, but they are there.
I see a lot of Subtle, Distance, Quicken, and Twin spells for metamagic as well as using swapping slots for points both ways.
Although versatility is also huge and always "on", you still need a long rest to prep new spells when you want to change them out. IMHO, the Wizard's ritual casting is their
REAL strength. Every other ritual caster needs to still have those spells prepared, and being able to cast them
without needing to prepare them is SO big for Wizards. Versatility is great, but 90% of the time the Wizard typically has the same spells prepared. I hardly ever change them out on my wizard unless I know I will need something, but I use ritual casting a lot!
Anyway, I think bumping Warlock and Sorcerer known spells maybe to 18-20 would be good. I don't know if going to 22 like Bard would be balanced--it might be too much. Of course, with our house-rule for Expanded Spells for Warlocks, they can know up to 25 spells, even if 10 are predetermined. With that in mind, really only Sorcerer's need a bump IMO. Maybe something as simple as start them with 2, give them +1 known spell per level, up to 17, and stop it there? Then they would have 18 spells and could do 2 per spell level if desired.