The OP seems to be asking about using Destruction as a primary source of DPS, so why are other classes even mentioned? They may have superior damage to a 'pure' mage class, but I'm finding Destruction to be entirely viable and very fun to play. I'm also playing against the game, not TES:V Multiplayer. (Keep in mind I'm only level 30, so I could be in for some unpleasant surprises later in the game.

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Granted, I'm running around in jumped up bathrobes and low level creatures can be extremely dangerous, so I must exercise some caution while pillaging Skyrim of it's most valuable and magical goods; therefore, I am very sneaky and hard to detect. Close combat usually results in a lot of pain, so I carry some potions to heal myself in emergency situations, and some restore magicka potions for the same. I rarely use them and don't craft potions, although I packrat like mad in case I decide to later..
I'm Dragonborn so I shout a lot. Projecting a whisper into the far corner of a cavern is a good way to provide for some misdirection. Power Word: Kill (heh) is a means of softening enemies up before I finish them off. Fus Ro Dah is often useful for additional stunlock if necessary. I rarely need anything more powerful than Firebolt to stagger and kill enemies, and low level mobs usually die in a couple of hits.
I do take time out of my busy schedule to trap souls, and in between tavern visits in town my hobby is enchanting Iron knives to amass wealth and skill.
The other schools of magic--sigh, I do use them. Healing while hidden has proved useful from time to time. Summoning a globe of light helps me find loot. Trapping souls for fun and profit--I've already mentioned it. Summoning atronachs is occasionally useful as a diversion (especially with Falmer), but I'm disinclined to share my company with others. I *am* starting to feel guilty about the dark looks Lydia has been directing at me lately. She's been gaining weight, what with all the cinnabuns she's been eating in my humble abode.
Eventually my labors with Enchanting will result in some seriously nice gear--I think I'll keep my Archmage robes--and Skyrim will learn the horror they have created when they tried, and failed, to put yet another Dunmer refugee to death.