Damage wont affect your resistance. If you had all your resistance close to 60% or above, you wont actually take much damage. My lvl35 warrior had 58, 52 and 58%+ resistance for melee, range and magic. When I take a potion of armor, all 3 will be above 60%. But actually the damage I taken also not much different. High difficulty divine and zandalor dealing 80+ damage on me, where as those paladin only doing 20+ damage.
When I kill divine straight with 1 thousand strike, basically I just wait for the 15 sec cool down and use it on zandalor again. In between the cool down interval, just kill those paladin around. If lucky enough, I dont need to spend a single potion or healing to finish the final battle, as my weapons life leech will help me replenish my hp.
The problem is now with legiondraconis, whether he has any save files before entering hall of echoes. With tons of potions, the battle shouldnt be able to finish even not well geared or skilled.