Would like to add that while it may be a measly 4 seconds stun to you, more often than not it can spell the doom of a DPS/healer especially when the fight begins to turn sour.

Those 4 seconds feel like an eternity to us!

But back to the topic. I too feel it's a little too powerful given the fact that a single tank, who already can change the tide of battle when played well, is given a skill that affects a multitude of players so drastically.