To me, the genius of the Nidhogg phase is that you literally cannot have single a death or dmg down on any tanks and dps (might be able to afford one healer death) because it would cause a snowball effect. Dmg down or death penalty? Well you aren’t making the dps check on nidhogg or eyes. Oh you melee lb? Well you aren’t getting pass time warp.
nidhogg is 9 different roles(3 debuffs x 3 numbers) with like 4 variations(in/out) on top of the memorized role. It's actually pretty nuts. I mean, some of them are only slight variations, but the fact that there are THAT many is kinda nuts from a prog standpoint. couple that with a pretty steep dps requirement and I think it's ridiculously hard, I agree
I believe Sanctity of the Ward and Death of the Heavens are in the same level of difficulty (maybe Sanctity is a little harder). The major difference is Sanctity is in the very beginning of the fight so it was easier to prog.