>>712789874
That's what I thought until I tried tanking. You're actually supposed to control the whole fight.
You're expected to know weird strats to position the boss in a specific spot facing a certain direction so their big AOEs are predictable or whatever.
You have to memorize phases and attack patterns so you know when to pop your 5 second invincibility move to block their instant kill move.
You're like the group strategist.