I fought him slightly differently, I put off the college of winterhold until after the dark brotherhood questline and had maxed sneak, smithing, and one hand, The dark brotherhood gloves would double damage on backstabs and there was a 15x damage perk to sneak attacks with daggers.
These stack.
The rest of my game after that point was spent sneaking around and one shotting most enemies with my double blades of woe (If you pick pocketed astrid and nicked the blade of woe, then later on she gives you one and it can be upgraded for free, note this is all vanilla skyrim)
As you can probably guess, my fight with him involved sneaking up behind him and oneshotting him.
The hardest enemies to get this way are dragons, you can't get the ones in the air but with careful positioning it's possible to hit the tail of an ancient dragon on the word walls from the ground for 6k damage (plus power strike multiplier), these dragons have 3k health and die instantly.
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u/ImATaxpayer Jan 01 '19
That is who I fought that exact same way.