To be fair, there were very real differences between 3.x Vancian and Spontaneous casters - enough difference to make the Sorcerer tier 2, in fact.
But, from a build-to-concept perspective the 3e sorcerer was actually a pretty good class. It's more or less fixed spells known meant you only had to stick to concept at chargen and level-up, there was never a temptation to ditch concept to prep the most expedient spell for the situation. While spontaneous was thought of (probably conceived of) as removing a restriction from Vancian and making the sorcerer more flexible (which it did in a round-by-round tactical sense), it also made it less flexible in a day-and-longer 'strategic' sense. Ironically, that made individual Sorcerers more unique and flavorful than individual Wizards.
Without that distinction (5e neo-Vancian characters have /all/ the flexibility of both 3e Sorcerer & Wizard, combined), the Sorcerer needs something else. Either a unique casting mechanic like it had in the playtest, or it's own spell list like it had in 4e, or something really remarkable hidden in those named class features....