Just echoing this. I run with about 4.7M hp flasked. I can live through a spear, but that's assuming I'm at 100%, which I am never at when I start running from a spear, because I've just been tanking him normally for 10-15s. The first spear is fine because I'll have Shield Wall up. The second one will kill me every single time. We could use an external CD for that second one, in which case, the third one would kill me, every single time, assuming that I'm using Last Stand for some other part of the fight (which is invariably required).
Seems ridiculous, I don't know.