In short, a Destruction mage is stuck at 90 damage Incinerates that do not increase in power, and are completely screwed when their mana runs out. Warriors, on the other hand, have no such problem, since they can spam auto attack.
I don't get it. This Destruction thing has been complained about all over the boards; it's fact that Destruction damage does not scale but melee damage does. It's fact that mages who rely on Destruction for offense are struggling to make it viable. It's fact that mages have to have -%mana enchants to be viable and as a result become FPS shooters stunlocking enemies to death with a barrage of low-damage spells. There are multiple people who say that melee is infinitely more viable than Destruction at later levels.
EDIT: And that unlimited times slashing argument doesn't even make sense. Autoattacks are a basic feature of melee classes; mages get no equivalent.
1) Incinerate does 198 damage (nobody casts it without dual cast).
2) Everyone complaining about damage scaling with skill has no idea what they are talking about. This is not a problem for destruction. Before anyone says anything, I'm not saying that destruction does scale, I'm saying that its not a problem that it doesn't. Yes weapons gain about 40% damage from skill. Destruction effectively starts with that extra damage built from the moment you get the spell. At 100 skill destruction spells deal far more damage than melee/bow attacks at 100 skill (no smithing, no enchanting, just 100 weapon skill and a daedric weapon). At less than 100 skill the balance is even more in favor of destruction. However, what destruction lacks is synergy with other skills. You can't use smithing to up the damage of your spells, and there is no enchantment to increase the damage of spells either. This is why physical weapons out-perform destruction spells in pure damage. It has absolutely NOTHING to do with scaling. People claiming it does simply do not understand the mechanics of the game.
3) Those who claim destruction spells do too little damage at high levels obviously haven't tried it themselves. Either that or they just want to run around 1-shotting everything. Most enemies die in just a few casts, even on master at lvl 48. Bosses take a bit longer, but still die pretty quick. Generally, I walk into a room full of enemies, spam my fireball at anything that moves for ~30 seconds, loot all the corpses, and then move on to the next room. If I use a sword sure I'll 1-shot most enemies, but it will take me longer to just chase them all down. Destruction does not kill too slowly.
The problem with destruction is that spells cost too much magicka until you have enchanted/found items to make it free then after you have done so magicka is trivialized which is kind of boring. Scaling and lack of damage are not problems at all.