I think that's been my point the entire time, there aren't many supplemental classes to destruction magic other than alchemy that help you deal more damage (like there are with other classes). With that said, how can you reach levels higher than the mid thirties without leveling other skill sets, if you don't use other skill sets you won't get higher and the creatures aren't as tedious and can be killed off. If you run out of mana you can always use potions and staffs to finish the fight.
Your whole point of argument relies on the fact that it's
possible to... "finish" the game within 35 levels.
the problem comes when someone actually plays the "Role Playing" part of their Role Playing Game, and levels beyond that
At which point, your whole argument is moot. People have already said that Destruction is just fine during the "normal" range of levels. Once you hit "high", Destruction no longer even functions properly except you exploit either enchanting or alchemy due to the high cost of magicka to cast them, and the low damage output ensures that you HAVE to. This pigeonholes everybody into playing a Destruction mage the way everybody else plays. The problem is not that people don't have the time to wait for Magicka to regenerate, or the money to use potions. They do, but if a skill barely functions if not supported by another skill, it's not "synergy", it's pure broken.
The argument by those who says it's fine is that warriors rely on armor skills and smithing to be able to survive. The problem here is that armor skill does not rely on smithing to absorb damage, nor do the weaponry skills require armor skills or smithing skills to be able to do damage. Smithing simply makes them do a better job at something that they're already good at, that's synergy. Now as for Destruction... either you lollygag until your magicka recovers, or you powerlevel enchanting and/or alchemy to make Destruction do its job properly.
And remember the slogan: "be whoever you want, play however you want". The current Destruction mechanism heavily severs the option for mages to deal damage the way a mage should: with Destruction