I had 1200 resist all with other equipment....I was tanking about half that Im tanking now. (About 6000 armor)
So what exactly are you saying? That there's a bug in which resistances are reducing damage by less than what they say they are? Otherwise, this makes no sense. 1200 res should have the same damage reduction as 12000 armor, so 6000 armor + 1200 res is clearly way better than 12000 armor and 40 res.
My resist gear had me with 20k health, ~6k armor and 1200 resist with buff from Warcry Impunity.
I was dying. Now I die much less.