Pets are buggy on some encounters, I would rather kill them than have to micro manage them. 0/21/40
Pets have spell travel time/movimentation, delay on target switching, micro manage, slow burst, buggy on a lot of encounters. Even with 1% less dps I would choose to sac it.
Sinestra, chogall, conclave, beth'tilac alakir, alysrazor, madness, were all important encounters on last expansion where pets were an absolute mess and waste of dps. Very frustrating to be low on damage charts due to pet bug/bad design.
You do gain some damage from the pet while not casting MG but then again, you do less damage when casting MG, so I'd say the damage is pretty much the same(It basically just means that the extra damage on Sacrifice accounts for the pets damage and vice-versa). This is without taking into account the fact the the best dps pet is the observer so you could lose damage from the pet switching targets.
Given KJC, the only time Supremacy pulls ahead of Gosac is when there are periods of time when you can't dps the boss but your pet can.
You underestimate your pets. On WotE an Imp can pull 9mil+ damage (obviously dependent on fight length). An observer can do 11+. When you're not casting MG much, that is a lot better. If you're worried about target switching, use the Imp. Otherwise use your Observer and stick it on the boss.