It's viable as long as you include alchemy and enchanting early on. If you really grind enchanting then you can almost completely dispense with the alchemy later on. I have a mage right now at level 30 with 100 in enchanting. I have enchanted gear that reduces Destruction costs to 0; and that easily makes for a viable Destruction mage. It does svck that damage doesn't scale with your progress but I've found that it works well enough so that it's still fun even though I don't have to manage my magicka costs when casting any Destruction spell. I also use Restoration, Illusion, and Conjuration, so I do have to manage those costs with a low magicka count (260).
It can work as long as you're willing to collect soul gems and soul trap everything in Tamriel that you can.
Actually IMHO it is better to concentrate on Magicka enchantments on wearables first, and destruction secondary, giving you about two or three enchantments for destruction, and 4 or 5 for Magicka (dual-enchanting). Using this method, I get a fairly strong destruction Mage. But max. strength Fortify destruction potions are still needed in tough fights W/dragons or large groups, even W/summoning or a follower. That's NBD to me, pretty easy to keep up the alchemy ingredients late-game. Of course, other max. strength potions are also recommended for the harder fights:
Fortify Alteration & Ebonyflesh (if you aren't wearing armor)
Fortify Health
Fortify Magicka
Regenerate Health
Regenerate Magicka (if it isn't a fast fight)
If vs. magic-use (incl. dragon):
Resist Magic (can get to 30% late-game)
Resist Frost, Fire, Shock
Using these, I can kill a dragon in about 3 hits of Thunderbolt (W/all but one perk in that branch, the shock branch) using both hands, no dual-casting perk. Usually kills other opponents in one or two shots, Draugr Deathlords in 4 or less. Lesser Draugr killed in two or three shots without potions. If I'm wearing the right clothes (I forget to change), I almost never run out of Magicka in a fight (using those potions).
So, to answer the OP, IDK, bc I only started playing Skyrim in March. You would have to decide for yourself from my report.
To other ppl: If you don't want to bother W/potions or enchanting, then either A. You shouldn't be a Mage, or B. You should lower the game difficulty level (do you know how?).