Wizards know more spells than sorcerers and have a larger spell list, but each day have to choose a subset of their spells to prepare. Thus they might prepare a spell that is useful for an encounter, or might not. Whereas a sorcerer knows less spells, but can 1.) always cast all of their spells and 2.) gets access to Metamagic and Sorcery Points, which they can use to buff their spells and get more spell slots. tl;dr, Wizards have more broad versatility but less power on any single day.
However, in BG3, wizards can freely change their spells at any time (plus you can rest anytime), removing one of the largest reasons for picking a sorcerer over a wizard. The ~only benefits of a Sorcerer in BG3 will be for the Metamagic to empower spells and the specific sub-class powers. And roleplaying.
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On the topic of Sorcerous Origins, I highly doubt that we'll see any non-PHB ones. Wild Magic especially seems right up Larian's alley, although they'll almost certainly use a shortened version of the wild magic list.
I'll add my +1 for Larian to implement them, just in case! Or at the very least, it'd be nice if Larian homebrewed the PHB-sorcerous origins to gain domain spells (additional known spells based on your subclass) just like the newer non-PHB sorcerer subclasses get. Larian likes additional options, right?
