Not sure if that’s intended or not, but the Imperial Pyromancers in the Soulfire Bastion dungeon do far more damage than any other enemy when you have the necrotic shield up.
I’m level 90 Spellblade and ran the level 75 dungeon, my fire resistance is at 70% and I normally can tank a few hits when the wrong shield is up. But the “Raging Soul” attack of an Imperial Pyromancer did 10,941 damage and as you can imagine there’s no way to survive that.
See screenshot of my death screen: https://imgur.com/a/dxeLMPG