I would say its more of a healer error. Looking at tank death's he was only taking 50k or so a melee, then falling down. Healers really have to adjust and the tank has to make sure he using cool downs very actively. 50k melee's aren't that bad as we see him hit well over 110k.
Also the void diffusion that hit your tank a pretty big no-no, make sure you group is adjusting so they are not hitting the tank because once its as large as 70k it will be a tank death.
[Today 06:48 PM] Ion:swimming in a natural body of water ISN'T acceptable...it's momentarily tolerable