I'm level 100 destruction playing on adept difficulty and i'm level 34, and it's not weak, it might be until you get to adept. Adept spells is when you get all the spells that hit multiple targets and do a god amount of damage.
You haven't even reached half the level-cap, and you will
never do more damage than you are dealing now with Destruction. However, the enemies still have almost fifty levels of power growth. That's why destruction is underpowered.
The problem is Bethesda decided to make low-level spells become long-lasting Tickle Lasers instead of magicka-sapping Armageddon-in-a-Fist, especially considering the unique nature of each spell. Ideally,
Flames would be a solid, go-to Short-range destruction spell. Unfortunately, the lack of damage scaling renders it functionally obsolete once you get "Stronger" spells, despite the tactical need of a kickass short-ranged Flamethrower spell.