To be honest I never have focus issues, only when shooting with the RZ67ProII with low key lights at the end of the day.
I've been using center focus for as long as I can remember, but I hear a lot of photographers complaining about it, maybe I'm just oldfashioned but I believe that if people could do it 20 years ago we should be able to do it now with brighter viewfinders.
However I love progress.
So I hope that it drips down to Canon, Mamiya etc.
It's always good to have something that could help.
About models moving 4mm, that's indeed not done, we use superglue and gaffer tape for that.....