I did some BC and LK timewalks and while the damage was quite high it was nothing that couldn't be managed. I think it is important to note that even 100% stagger isn't instantly lethal. In the past high staggers like that were quite dangerous because we still took at least 50% of the damage directly even with high mastery.
But now we have 75% stagger with IsB up so while stagger ramps up quickly there no immediate danger when it rises. Using this knowledge and the Blackout combo stagger delay made timewalks quite manageable and fun. The trick is to get most out of the purifies.
Having/Using T18 set bonuses is important and helpful too. 2 set generates a lot of orbs and they heal a lot in TW.