Not using Dremora isn't a weakness since you have Odin.
For more variety to your build I would incorporate more Alteration spells into battle if you don't already, not just the perks. Maybe add Destruction since it has synergy with Atronachs both inherently and in the Conjuration tree. (Personally almost all my mages use Destruction, even if it's just a minor. Because sometimes you just wanna melt a fool.)
Without an encounter zone mod, a level 35+ character is approaching the point where no enemy poses a challenge (except maybe Alduin, Miraak, and the Ebony Warrior). That's just how it is. The answer at that point is to up the difficulty and/or mods.