However, the Rupes is a very smooth machine and can correct fast(as long as the pad is spinning).
I know the thinking with a traditional DA is it doesn't offer much correction unless the foam pad is rotating (in addition to oscillating).
That situation might be different with these large throw machines, which weren't around when that traditional thinking was developed.
I'd tend to think, with 21mm (roughly 7/8 of an inch) of orbital diameter, you're still getting a fair bit of correction due to the orbital motion, even if pad rotation stops.**
7/8ths of an inch is about the same size polishing circle as you'd have if you were spot buffing by hand with a small pad.
I don't think this point necessarily holds for smaller throw diameter machines, just because many pads have more stretch in them than the orbital diameter. So if the pad face is stopped in those cases, about all your're doing is exercising the internal foam by stretching it in e.g. 8mm diameter circles, but most of that motion doesn't make it to the face of the pad.
I guess a person could test this by doing a "reverse washer mod" so to speak, where the pad is prevented from rotating at all, but still moves in its 7/8" orbit, and comparing to the same rigging of a small throw diameter machine.
But the choice of pad also matters for this test, as far as stretchiness without tearing. Rupes pads do seem to have less elasticity than other foam pads I have, so maybe this was a special design consideration in matching their pads to their large throw machines.
**one case where this might not be true is if the machine is driving you, rather than you driving the machine. In that case your arms are absorbing the orbital motion.