Mutilate just got nerfed. Might want to rethink that statement.
To answer the op, you have options in phase 4, but if you are raiding mutilate will probably still win out because your raid team will want maximum occult poison up time. The only real way to do that is to run the deadly brew rune on your chest and use mutilate. It is possible a backstab build could come close with the lower energy in phase 4, but mutilate will almost always get 5 poisons up faster due to proccing off both hands for the attack. All that said, with the change to poison knife now essentially making it a free attack it might be possible to get the poisons up quickly enough.
I am not sure where the theory craft has landed on rogues with the new changes to slaughter from the shadows and the hand rune. I heard the output might be higher in a vacuum for that style over a poison based mutilate approach, but unless it has a way to get occult up quickly and sustain it, I am not sure the individual damage will trump the overall utility.