I am puzzled when you state that the clubhead arc is likely to be less circular than the hand arc because of the following problem - the everchanging distance between the left shoulder and the clubhead.
I suspect that you don't spend much time studying golf swings using a swing analyser program and that you don't plot the clubhead arc and hand arc to see what is really happening.
The clubhead arc is amazingly circular in reality, compared to the hand arc.
Here is a strobe photograph showing the clubhead and hand arcs.
Note that the clubhead arc is much more circular than the hand arc.
Here is a composite photograph of Aaron Baddeley' swing.
Note how circular the clubhead's path is in space -despite a varying distance from the clubhead to the left shoulder.
I have previously posted photos of the hand arc of Tiger Woods, which shows an U-shaped hand arc.
Here is Sergio Garcia's hand arc.
Even when taking into account the camera perspective distortion problem (due the camera not being perpendicular to the plane of the clubshaft and the plane of the hand motion), it should be readily apparent that the clubhead arc of a good golfer is more rounded than the hand arc.
I suspect that you don't spend much time studying golf swings using a swing analyser program and that you don't plot the clubhead arc and hand arc to see what is really happening.
Yeah, and I'm sure you never looked at an x-ray during your residency.
I've only given about 13,000 video lessons in the last ten years. I hope I can learn how to use the software before I start getting really busy.