Yes, I think perhaps Impulsive should be (possibly) assassin only and have nothing to do with casting.
I think currently Fireball sucks for low Initiative champions and is boss for high initiative champions.
-> Instead it should be a good spell regardless of Initiative, imho.
Maybe turn Initiative into an Action points system, and have higher intelligence make spells cost less initiative?
Therefore things like Impulsive won't let you do crazy things with spells, because its your intelligence that matters more. Then Impulsive would be better for Assassins/Melee characters.