The 85mm 1.2 is a very special lense... maybe sometimes people don't understand the meaning of "fast lenses", this is no regard to the Autofocussystem
The usual use is for portrait or fashionphotography, so the model is (normally) not running through the picture like a small child.
As I also work with older MF-cameras, like the Zenza Bronica ETRS... where everything is about manual focusing, I never complain about AF_Speed, anyway. Composing an image is something different from shooting action events. I would be angry if the AF-Speed of an EF 24-70 2.8L II wouldn't outperform other lenses, but not on this lense.
The only thing I have to admit is that not everyone is able or fancy to get such an expensive lense. I myself always dreamed of having one and it took me some time to get hold of it (I shoot for fun, not for money). So, I think the sigma is a really fair packet, but on the other side, there is one hell of a 85mm 1.8 from Canon. And if you don't need the 1/3 stop on 1.2, so why bothering about the 1/3 to the 1.8