Lightning = Massive single target damage
Fire = AoE damage
Ice = CC
Over
Lightning = Elemental damage with lightning graphic
Fire = Elemental damage with fire graphic
Ice = Elemental damage with an ice graphic
Yes, lighting is our primary damage for the current TWO primals and probably will be for most boss fights. Melee classes only have one or two combos that do most of thier damage, so what? I use ice spells all the time on moogle fight and if you don't you might reconsider playing THM as a main. In DH, I use fire and ice all the time on all the non-boss monsters. I happen to like that the elemental spells are more than the same spell six times with different graphics, adds flavor to the nukes.