Unless it leaves you over the hit cap, gemming hit allows you to get more crit or haste.
What is wrong with his damage OP? He's not padding, is that what you want to see? He's second on weapon damage, and middle of the road on garrosh damage. He's using treents too, seems like a sharp raider to me; cares about getting the job done, not padding with add AOE.
The only thing he's messing up on is sunfire dot uptime for some reason. It's 10% lower than moonfire uptime.
I'd be pretty damn pissed if my raid leader did something like this, there's no reason to call a raider out publicly when he's NOT last on damage.