sure it eats up a lot of magicka, and if its not enough to kill your target quickly, there are alchemy potions you can have ready that boost destruction spell damage, ive made one with 94 alchemy and no enchantments boosting potions made that gave a 60% boost to destruction damage. so now you're looking at ~320 damage dualcast, 130-140ish single handed.
add in the max alchemy boost from enchanting that will be ~120% boost to damage resulting in ~440ish damage per cast. is it really that underpowered when you include what appears to be destruction magic's real support skill, as opposed to using just enchanting to help with it?

