CapnZapp
Legend
My argument is that you could take away the 5E PHB, rewrite it completely, but still keeping compatibility (more or less anyway) to the MM and DMG.This is one of the areas I found least satisfying with 5e. Our group played through Curse of Strahd and I found no joy at all from character creation or levelling up. I can totally understand how others may prefer this simplicity, but to me, it was pretty boring. We haven't played 5e since. It's just not for me. I feel it removes an enjoyable component of the game - crafting and personalising your character.
Thus making for a much richer deeper player-side building experience, but without significantly complexifying the game for the DM!

If WotC were to print an "Advanced Player's Handbook" with a set of new classes that weren't primarily designed to co-exist with the PHB classes, they would naturally need to call them Warrior, Thief, Magic-User or somesuch to not invalidate the PHB.
For Paizo, things would be simpler. A same-same-but-different game just doesn't have that concern. A Pathfinder 2 game does not need 100% or even 95% compatibility to 5E. In the same way Pathfinder 1 met with success even though it diverged from 3rd edition in a thousand little ways and even a few bigger ones.
This would appeal to the millions of current gamers in a way the clusterfrak of a PF2 playtest never will.
They could do a vaguely-5E:ish game, that does 5E better than 5E. A game where the DM's job weren't significantly more cluttered or complicated (primarily by not demanding full PC rules for NPCs!!!) but where the player's side, primarily during character-building, were just that: significantly more cluttered and complicated... or what we would say: much more involved - richer and deeper

They would never be sued since by now Paizo knows better than to infringe upon WOTc's remaining IP. And for the rest, they would just point to Pathfinder 1 and say all concepts are taken from that game, their own game.