It is slightly less perk efficient etc, but here is the 2 key points:
as long as you stay focussed on raising destruction constantly(not powergaming it though) by combat usage or purchase of training, then you are usually ok for damage/mana till early level20s.
AT THAT POINT VENDORS AND LOOT DROPS START DROPPING -15% OR -17% DESTRUCTION GEAR QUITE REGULARLY. YOU HAVE FOUR SLOTS, FILL THEM WITH THE BEST DESTRO GEAR YOU CAN.
AS YOU FURTHER LEVEL UP DESTRUCTION THE QUALITY OF THE VENDOR/LOOT GEAR RELEVANT TO THIS SKILL GOES UP, SO YOU JUST KEEP REPLACING WITH BEST AVAILABLE. you use your other slots for whatever you want. maybe switch out to other gear as necessary, c'mon a bit of inventory management never hurt, you are gimping your fun with level 100 dual enchants...
by level 30+ you should easily have 75% off destro spell costs, and your -50% cost perks are more than enough on all other mage skills anyway.
as you raise destro from 75->100 the gear availiable rises to -25%. you can get 0% with four slots without any enchanting. As for other skills, well, alteration spells are pre-combat, illusion spells are deaggroers and resto- only novice perk needed. destro and conj are the only ones you need to seriously put cost reduction perks into, no big deal. is a fair trade with 8 perks into enchanting for all the adventure svcking gheyness that brings.
I found this essential to putting the fun of loot discovery/earning money back into the game. cause i found the enchanting route left me with all the best possible gear by level 25 and the double slot enchanting made everything just too simple to resist stack/ cost decrease. raising to master doesn't help this at all tbh, just makes the game tedious.
btw, for custom difficulty where enemies do more damage and you do too, but without the tedious damage soaks, roll with pure mage no health increases/buffs and no armour/resists whatsoever or alteration armour effects/perks...on Adept or Expert. I found that gave required difficulty and yet avoided tedium as i was still "awesome" . If you avoid enchanting and alchemy, and stick to shop items, a non-sneak attack archer with legendary daedric bow does 200 HP per hit, at lower RoF that your damage selectable and armour ignoring 200 dmg per hit expert spells. 2H do 200per hit but no range, Dual wield do more but you are locked stationary. all suffer from enemy armour effects quite a bit. tbh the only issue is that spells don't get a sneak bonus, which would be fun. Even at level 50 , 200dmg ignoring armour, with stagger is better than almost any other direct weapon in the game(max smithed) in open combat. only enchanting/alchemy/smithing combos break this. Doing more than one craft skill is a bit lame for me personally though. power attacks and sneak attacks are available outside of magic, but destro has range, speed and stagger, can switch to weakness exploiting for extra damage, and ignores armour. It is balanced fine, the only issues is that the lower and mid level spells are more "interesting to use" than the higher lvl ones(which you rely on later). And the problem with AoE aggroing friendlies , or killing them...but that adds flavour i spose, so no issue there.
tldr: use shop bought items and loot, pay for some destro training at times and don't obsess over perk point efficiency. you will still be able to perma destro everything eventually, and along the way will have enough mana to get through anything without too much issue, and retain some minor challenge to mana conservation. YOU WILL ENJOY THE GAME MORE THAN IF YOU USE ENCHANTING, TRUST ME.
...and i didn't even mention that responsible use of alchemy(no cross pollination with enchanting etc) and some hunting for alchemy gear and you can near double your damage to "easymode" on any difficulty setting. personally i couldn't be bothered with alchemy, didn't need it.