I agree it makes spellcasters useless if anyone can use Scrolls.
I agree. There is also big side-effect of this issue that Wizard is able to learn any spell from scroll, even those not on his spell list. So now I have Wizzard in-game which knows and cast Guiding Bolt and Bless.
I am pretty sure its a bug, no way they intended for you wizard to become a cleric as well