Hi,
I'm not too familiar with power reverse. Sort of like I know basics on the power steering on my car.
That said, taking in the stories of power reverse creeping and with slop, I'd conjecture that all power reverse had slop. They would drift or creep out of position after a while. With a switch engine constantly changing direction, I suspect the creep would not be noticeable - the Johnson Bar being reset frequently.
As for road engines, it might be just a little related to how far apart the water towers were. Coming to a stop and restarting after water would be more like a switcher. The locomotives with large tenders (first come to mind is the PRR so called "Coast to coast" tenders - very long) or canteens (like Southern calls extra water carriers be it a tank car or a spare tender), and the creep would be noticeable. I would not be surprised to find out there was a way to reduce or eliminate creep.
FWIW
Doug vV