It's better to have the ability of f1.2 and only occasionally need it than to not have it and need it. Yes, the DOF can be very narrow, but that depends very much on your subject size, subject distance and image viewing size. So, a large subject matter shot wide open on a 85mm f1.2 lens at say 10mts, allows you to isolate the subject well yet have sufficient DOF at say "normal" viewing distance and image size. This is also dependant on what you are trying to achieve and even at say "relatively close" subject distance you may really want to limit DOF for creative purposes with the other above aspects of viewing size and viewing distance taken into consideration.
Example. These are the same size images, the same viewing distance but two vastly different subject sizes and thus subject distances are almost right as a comparison in order to illustrate on the 50 f1.2S lens.
1) An Australian King Parrot decided to fly into our home looking for food - must be very used to human interaction ( and hungry!) as it was very tame but not a pet. It even sat on a plate of seed and allowed me to carry it outside so as it wouldn't get slooked and fly into our windows and hurt itself.
Z7II + 50 f1.2S, 1/320s f/2.0 at 50.0mm iso640. I used f2 and not wide open as I was so close that there was going to be too little DOF at f1.2. As it was, I barely got the beak and eyes in focus but the background is so beautifully smooth and lovely.
2) A Wombat, which is a much larger animal, means that to fit it in the frame I need to step back much further and to get the isolation, f1.2 is just enough to get the background blur and isolation decent - eyes and head in focus and the background nicely OOF.
Z9 + 50 f1.2S, 1/400s f/1.2 at 50.0mm iso64.
It's all about the right tool for the job. If I were to use the 85 f1.2S instead of the 50 f1.2S, I would have to back up about 60% and I would quite probably have slightly better OOF blur but a narrower FOV which may or may not help in these situations depending on what you are trying to achieve.
Whatever the case for use, I would like the *ability* to choose the DOF for the occasion and be less limited by having as large a maximum aperture as I can that gives a balance of lens size, lens weight, lens cost and lens overall IQ. What that balance is for you may be different from me, but then we have the 85 f1.8S which is also a *stunning* lens as an alternative if the other parameters do not suit you. I have the 85 f1.8S and one day I hope to get the 85 f1.2S when more sensible street pricing comes about as it is way too expensive for me at the moment in Australia at AU$4,800!!!