That's a lot of damage. I'm not entirely sure why Sweeping Slash is hitting you that hard if you only have 1 stack. 4+ stacks, yes, I can totally believe it, but not 1 stack. One thing I can think of is that the bleed should have been cleansed faster. I don't think he does Sweeping Slash immediately following the bleed, so you shouldn't quite be taking that much damage all at once. Removing the bleed brings your 31k damage window down to a (more manageable) 25k, which should only be about 65% of your maximum HP, assuming you're using your Ultimate coms. That's not really all that bad. Your healers will have plenty of time to react. Make sure you pop a cooldown or adrenal when your health dips below 30-40% and you should be alright.
The tanks do get spiked very hard in this fight. Healers just need to be really on top of it.
Even if the bleed effect is cleansed and he only take 25k damage, that's 25k damage in the span of a global cooldown just from the boss's basic attacks. Tell me of 2 healers in an 8 man run that can heal 25k damage in one global cooldown. I can understand if the damage is from a mechanic like EC Kephess Breath of the Masters and such that can cause a one-shot, but that damage is from basic attacks only. Just seems like too much damage is going out from my perspective.