Good job. Too bad it's already been proven that NPC Mages damage increases as they level, whiles yours doesn't, right?
Sounds like somebody's got a case of the Mondays!
Yeah, NPC damage can easily get out of whack relative to the PC. I think it's pretty silly. Is the solution to make Destruction damage scale? Maybe. But currently, you can increase your Destruction damage via dualcasting (with the perk), augmented x (perk), and potions. Coupled with a focused build, geared toward Destruction, you can do fine. I play on Adept, but I've heard people who play on Master say it's doable.
To me, this setup is preferable to the boredom that quickly follows with a ridiculous damage-output uberlymaxxed melee character.
Currently, Destruction skillups yield more efficient casting. That is the way it's always been in TES games, at least since Morrowind. To deal better damage, you get better spells, use potions, and now in Skyrim, get perks.
It does require a different playstyle than other kinds of characters. Yes it does.