That's a problem with smithing/enchanting/alchemy synergizing too much to the point of being broken.
Now, I'm not saying Destruction is fine, I haven't tried it, but pointing out the other combat skills get ludicrously high damage is not evidence that Destruction is underpowered. It just means something is broken with those other skills.
Now, if someone using one-handed weapons w/ a reasonable level of buffs (meaning: don't go and min-max the system to exploit a broken mechanic) is still able to kill targets much faster than a Destruction Mage, then that is better evidence.
That said, one argument that is valid is that just as warriors depend on more than just their 1 offensive skill to succeed, the same should be true of Mages... and it is a fact that a pure mage who invests in multiple schools will have a lot more options available than a warrior (beyond simply blasting with destruction spells).
Itkovian
I agree that the issue isn't how powerful warriors are. It's really balance against the content that counts. My mage isn't high enough level to judge for myself, but it certainly sounds as though destruction has issues at high levels. Mana needs to be scarce enough to motivate us to use good tactics (maintain awareness of enemy resistances, etc.), but not so scarce that you avoid using all but your cheapest abilities or so that you feel forced to use companions because your character can't go the distance alone. Your spells should be tuned to hit the sweet spot where you can feel both powerful and challenged.
For me a big part of the destruction problem lies in the loss of castable debuffs. Different delivery methods offer some tactical challenge but I favor combining spells, whether at the spellmaker or on the fly. For one thing, we'd be less perk-starved. One handed has a many perks as destruction, but so far as I know the game doesn't include mobs with high levels of resistance to sword or mace damage so that melee need to perk multiple weapons. A mage who doesn't perk multiple elements is going to encounter far greater problems.
Also mages are the most physically vulnerable, have the highest expenses, and are the most resource-dependent archetype. When we first encounter an enemy it takes a bit of time to mount our defenses (cast our armor, etc.) I think we should be rewarded for overcoming those negatives with the ability to deal enough damage that we feel good about the strength of our characters. I know that's a very subjective measure, but I think that ultimately it's the one that counts.