They aren't unusuable, you just basically choose whether you want to use SoDs or if you want more bonus spells.
Int you just need to be able to hit 19 at level 17.
Wisdom could no longer be a dump stat for arcane casters.
Charisma can still be a dump stat for divines. (Persisted divine power doesn't care how ugly you are)
Of course, now you are free to maybe make a physical stat your primary. Now the Wizard can be stronger than the Fighter without polymorph.