Rather than interject my opinion I will ask a rhetorical question.
With a flat left hand we have the same RPM. For all hinges, but the "surface speed" or ratio of hand speed to clubhead speed is greatest for horixontal hinging, angled hinging is in the middle and the smallest retio for "true" vertical hinge. But if the ratio's are not the same how could it look the same from the center of rotation? It can't. So it won't?
Interesting, Hummm?
HB
It is obvious some do not understand the difference between absolute and relative- we are dealing with velocity here and the differences that are distinguished by their relative values. That is an impoprtant distinction for everyone.