DESTRUCTION DOESN'T SCALE. Again, this point has been made as well. It's probably the main point that is made. But let me summarize: once you get your expert level spells that hit for 90 damage with perks, or your master levels ones that hit for somewhere in the mid 100s depending on the spell, that's it. Your damage will never ever go up again. Now, someone in a thread before calculated that destruction can do around 146 or so damage per second with these numbers compared to 500-600 or so for one handed. That's fine for lower levels since, as many people have argued, 146 dps is more than enough to kill pretty much anything the game throws at you, and so the discrepancy doesn't matter.
But once your enemies start actually scaling in appreciable amounts, it becomes easily noticeable how weak destruction is.
I realized this as I, a level 60 mage, was running through one of the dungeons with a dragon priest at the end. These dungeons are in general supposed to be much harder than your simple bandit dungeons that you crawl through for miscellaneous quests. At the final fight, the dragon priest popped out of his tomb/sarcophagus along with about 3 draugr deathlords. Eh fine, no problem.
But then, more started coming out in a staggered fashion. I expect this was meant to spread out the amount of enemies you would have to fight over a longer amount of time, but it was taking me around 15 incinerates (the highest damaging single target spell you can get) to kill a single deathlord. Because of this, they started coming out faster than I could kill them, and I ended up with 6 deathlords + the dragon priest on me by the time they had all come out. That's over 100 casts to clear the entire room of them, which is not only ridiculous but impossible to manage without the -100% casting enchant from a fully maxed enchanting tree. One tree shouldn't absolutely need another tree to function, much less require 100 skill in that tree (which is required to get -100% magicka reduction).
To kill them all, I had to either back track through half the entire dungeon to keep them all from piling on top of me as I tried to kill them, or use the mass illusion spell mayhem, which caused them all to fight each other leaving me to sit there and watch. Which wasn't a problem, mind you, but it made me realize how ridiculously weak and slow at killing things destruction is at higher levels.
This is why scaling needs to be addressed. Again, for the majority of people who will never level up that high, 90 damage is more than enough to roll everything and complete the main quest without trouble. But if you like to explore or train other skills at all, and level up fairly high in the process, you will see why destruction needs to be fixed. Please address this Bethesda.