2) If you are CC'ed, pets can still do damage while you cannot. Notice how GoSac does not buff DoTs, but only direct channels that require you to be active?
3) From a PvE point of view, same goes for movement. None of the abilities buffed by GoSac can be used while moving. Hint: while there is no movement in DS there is a LOT of movement in MOP. This means the more movement, the better a pet (which incurs no movement penalty) is. (Note: how many times have you heard a vengeance tank topping meters cry about not balancing around "old content?")
4) GoSac does not buff AoE whatsoever, so actually having a pet means better AoE than not having one (assuming you have a single target pillar).
5) GoSac doesn't even affect two-target damage, so the less time you are actually casting your single-target channels, the better pets are.
In this sense, for patchwerk, Grimoire of Sacrifice actually should be top DPS. Because in every other scenario whatsoever, it's not. And I'm actually concerned the spec itself will be bad if people are overeager when it comes to nerfing it simply because it performs well under the most ideal conditions, of which there are none in MOP.