To me, the physics part of this debate is very interesting academically - but as a defensive shooter, it's much more the subjective "felt/perceived recoil" that concerns me, as it governs how fast I can run the gun and get shots on-target.
Towards that end, Ljutic, I believe that "spin" you're seeing is a path-of-least resistance phenomenon: look at how your support hand comes off the gun. Then watch these often-cited reference videos:
https://www.youtube.com/watch?v=NVhTA-n0ivE <--- Travis Haley's great opening lesson on grip basics, via the Magpul Art of the Dynamic Handgun DVD series.
https://www.youtube.com/watch?v=_O-Wedt3N4U <--- Mike Hughes of Next Level Training, takes us through his high-speed footage.
From your high-speed vid, it looks like that's happening a bit with both the Rohrbaugh and DB9 a bit, too - and I believe that the former is more due to just how small the gun is and how much harder it is to hang on to: but look closely enough at the PM9, it's doing it, too, simply because on guns this small, we as adults with even average size hands do have a problem maintaining a solid two-handed grip on them.
Awesome stuff, thanks for sharing!!!
The worst recoil of any handgun I've ever shot was a S&W airweight in .357 Magnum. It also gave me the erie feeling that it might come apart under the abuse. Besides the pain it inflicted, there were two very important problems it presented. It was impossible to follow up a shot with another well placed shot in anything like a reasonable amount of time. It also blinded anyone close to it when shooting in low light.
I think Hickok45 had a very good test on his youtube channel comparing recoil of various rounds. There was not so much physical difference shown. I agree that shooter perception of recoil is something that must be overcome. For me, I've never noted much difference between 9mm and .40 in equal weight guns. Smoothly overcoming recoil is the secret. Remember: Slow is smooth and smooth is fast.