Conjuration doesn't really scale like Destruction does, tbh. Your Dremora Lord is doing okay damage but you're right that it feels more like a distraction tool, especially on higher difficulties. The thing is, summons cap out pretty hard because their damage is based on your conjuration skill at the moment you cast, not dynamically - so there's no "scaling" the way you'd get with a destruction mage leveling up Fireball.
That said, the perks that extend duration are definitely worth it over the corpse health ones. Keeping stuff summoned longer means you're casting less often, which frees you up to cast actual damage spells or use a weapon. The reanimation health perks feel like a trap - your corpses die anyway, so why invest in keeping a corpse alive longer when you could just summon a fresh one?
The real damage ceiling for conjuration is just accepting it's a support school. Dual Dremora Lords trivializes stuff yeah, but even one well-placed summon + you casting Mayhem or a solid destruction spell = way more effective than just watching your summon solo a room. On Solitude difficulty at level 22 that's probably the sweet spot you want - summon something tanky, then nuke from range while it holds aggro.
If you're on PC and want conjuration to actually feel like a real damage source, there are overhaul mods that rebalance how summon scaling works, but vanilla Skyrim just doesn't give conjuration the tools to be a primary damage dealer. It's designed as a utility/control school.
