OK I see your point, I am a little worried about the offensive ones myself.
About the more defensive ones.... what about limiting it to self. So like Clerics (in my example for earth) could cast stone skin, but only on self. or for Air could cast displacement but only on self.
Would that be better?
(By the way, I almost threw in the spell haste to the Air Domain and took out the 2 damage spells, maybe that would be a better route to go.)