Garrosh takes a brain to do, you can't just blow through it.
It's pretty simple if you have a well-rehearsed raid leader who can shout specific instructions at each given stage of the dance. That's all Garrosh is; a long dance. You move in, you move out, you move to the side, you move in, you move out, etc, etc. So long as everyone can follow simple directions, it's a piece of cake.
That said, I don't think every endgame boss has to be able to be beaten by PUGs.