Bosses melt with tanks just as fast as with DPS because of powerups.
Off the top of my head
+25% damage when exiting prowl
+15% damage when taunting
+50% damage while channeling convoke the spirits
Add in the other +% damage done and the potion.
I wouldn't underestimate tank DPS at final boss. Specially because we can focus on getting single target powerups over survivability/AoE (against trash mobs).
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Thrash and Swipe are so satisfying