Let's turn this back to being constructive:
What is damage mitigation?
To me, damage mitigation is simply a reduction in damage taken. Be it avoiding being hit, increased resist to take less damage, damage eaters, stuff along those lines. There is SOME merit to the idea that the quicker something dies, the less damage you take as well- but, I really don't consider that damage mitigation.
I agree with both of you on this front. The only situation where I'd disagree is the not-entirely-theoretical scenario where you can take a 1-hit kill. If something lands a Blood Oath in the tick immediately before (no chance to tab in out) you land a max damage double strike, well, you're going to die. I'm not aware of any monsters that can regularly hit for a killing blow.Yes!
This is why I counted damage taken per minute.
For me it's all about RoT. I've tried running a VE + 100 HLL against things that hit really hard. Yeah, it helps, but there's still quite a lot of volatility to it.