Do we really need One Spell to rule them all?
From sorcerers/wizards get wall of fire until they retire, my bet is that the vast majority run out of level 4 components faster than any other, and that the vast majority of level 4 spells they cast is wall of fire, it's just that useful.
Given that wall of fire is so hugely popular (because it's powerful), I think it's perfectly fine to take it down a notch. Even though my wizard will be a little weaker, who knows if it will be more *fun* to rely on a wider array of spells?