I'd like to know if my thinking is wrong here. I want to maximize the damage output of my mage on Master difficulty. As I understand it, my opponents will get more hitpoints as I level. Thus, the best plan is to maximize my damage output, let's say Destruction to 100 with many perks, but do not level any non-essential skill.
I've already completed the main quest with a level 46 dunmer mage on Master. However, I did not make any special effort to slow leveling in lockpicking or any leveling from skill books. Therefore there are probably several levels where my opponents became stronger, but I did not increase my damage output or even ability to survive.
Do I have that right? If so, when I play it again, I plan to have a follower open all locks (I was halfway through the game before realizing this), and ignore all locked doors that cannot be bypassed with the Tower. Also, I will not turn in any quests that level any non-mage skill and also not use any skill books that level the wrong skills. I'll hit the Mage stone right away too.
Single-target Destruction damage caps out at 70 skill when you learn the Expert level spells, but your Conjuration summons can add their own significant DPS (2 x Dremora Lord). You can then work on Alchemy to brew some potent Weakness to Magicka poisons, which can be applied to tough enemies via bow for extra nuking power.
Don't avoid leveling up, but make sure that you're purposefully leveling either Destruction or Conjuration a bit with every level.
They don't just get more HP and hit you harder, they also start being able to be too high for your Illusion and/or Alteration spells. It's super lame to have mobs resisting your Calming spells when you have 100 Illusion and every perk you can grab. I know not everything gains levels as you do, but I know that my Pacify worked on guards when I was in the 30s but when I got into the 40s they became immune. I hated it. Punished for increasing your skills? Huzzahhh...
Do you have Kindred Mage and Hypnotic Gaze? Did you try dual casting the spell?
Kindred Mage + Hypnotic Gaze increases the spell's maximum target level by 18, and dual casting it effectively doubles the maximum level.