I agree. When we first started working on this fight, our arms warrior rended, tclapped and then bladestormed.... that equaled a dead warrior.
The key was to have him hold off until you get rend on everything and are starting to kite them. Once you have them all rounded up, you can throw vigilance on him (as the MT isnt getting hit technically) and taunt back if he grabs anything.
That particular fight has a LOT of damage on the OT with the Adherents, especially when you have 9 of them up. Of course, you want to kite as best as you can so to not take damage, but survivability is an issue. I wouldnt stack threat stats in exchange of mitigation or avoidance on this boss.
Deeps for show..... tank for dough.....