@epurator
Tips From what i have done:
Recurrently, Boss “Collapsing World” are close or same time as Portal spawn. So in those case, we should bring the boss opposite side of Portal Spawn in order to control/stun/cleave adds.
Few combo are deadly: Bring boss + stack + Line to avoid. particularly at the end of the fight + Destack.
That is one of the reason 3 tanks make it smooth as it is not a DPS check fight.