From what i've seen so far, bosses enrage at about 50% hp, at which point they become untankable, can anyone actually compete them?
Yep, better dps. We had last boss of BT at 10% before she enraged, but our tank popped all his CDs and we downed her. Some of the fights are somewhat prohibitive on DPS requirements, but are mostly doable. If you're jumping into hard modes right at 50 while wearing level 40 greens, you're going to have a problem. Run BoI/FE a couple of times to gear up, get some craftables, and go back later.