I don't get it. Why is my survivability garbage?

[SeCKSEgai]

And this is after I put a nearly 3k defense Duress Ornate Plate on him. :(

3k def means little without a nice multiplier (frozen armor, defiance) hence while fort is so nice, ED and Def.

[SeCKSEgai]

Oh, just went back into Nil's lair for the first time since last season - totally forgot about the bugged damage poison clouds from the vipers - those are easily death traps for merc, and you if not careful.