Good post and 100% on target. Hatestorm has been a thorn in this mod's side for a long time with his very erratic dmg patterns. I got to the point on HC where I just lured him, parked him, and moved on when I was at the appropriate level. I believe it is something with is blade skills that triggers the mass dmg spike that wipes a character out. All I know is that it has been around for at least 5-7 patches without a good fix. I think it just has Soulmancer stumped.
Korlic is an entirely different situation. His leap attack is what is doing the big dmg hits and you can avoid (for the most part) by standing right at his toes and engaging him in melee. This of course is tricky with the other guy spiraling whirlwinds at you, but hey - life is full of hard situations
The issue started when Soulmancer buffed the Leap Attack skill to epic proportions which makes for a really fun barb build, but a really nasty Ancients battle.
Also, now that you know it is the leap attack you can try to be fast on your feat and avoid it when he comes down. That isn't an easy thing to consistently do, but perhaps you can give it a whirl.
Happy gaming!