stop stripping tanks skills and abilities and adding them as role actions

[Megguido]

Either Megguido is right, and your timing on cooldowns was off, or you suffered an additional auto attack right after TB hit you.

I am pretty sure, you wouldn't even lose 50% with iLvl 340 and Vengence+RI. Parties cleared that fight with old Alex/Shire Slaying accessories and iLvl 310 body gear, and they still survived TB even without Invul. They were ~40k HP or below, especially those with no VIT melds.

You just can't lose 75% of 82k HP on iLvl 367 with a CD (Rampart or Vengence/Shadow Wall/Sentinel), and no auto attack after. Get your Co-tank to voke earlier (pref. during TB cast).

That or he's tanking with the slashing debuff that follows the previous tankbuster (well, on susano specifically).