All right, could you take a look at this then please so it's not just anecdotal? Running just Demon Spikes when the spear hits me, I was getting hit for 4.5 million. Besides not being healed to full (ignore being bad, fight is kind of rough in 10H), what else should I have done? You can see how far I was here. We tried the strat where one person just stays further away and taunts to get afflicted with the debuff. I think logs processed the death weirdly cause you can see I cast Demon Spikes 3 seconds before I died and was even in metamorphosis.
Is there something funky where you have to cast active mitigation/cooldowns when he targets you with the ability not when it hits you? I'm really at a loss for why DS + EW alone can let you survive in mythic where DS alone hits me for more than max HP in heroic 10.