Nice comparison (though fairly predictable). As far as the Gen4 vs. Gen5 G23, I suspect the difference was fairly arbitrary given so few rounds, OR, the finger grooves (or lack thereof) made the difference.
When I think of "recoil" between different pistol loads/calibers I think of recoil as pushback and muzzle blast (not just muzzle rise). Both are always being felt, but depending on the bullet weight and the charge we feel one or the other relatively more than other calibers/loads.
Faster bullets tend to be snappier/flippier, and heavier bullets push back more towards the shooter (because of Newton's Second Law). So for example, I've heard people say .357 SIG has a lot of recoil compared to even .40 S&W (e.g. Hickok45), but you have to look at the bullet weight and power of each round to make a fair comparison. When you shoot a 65 grain Underwood Bullet traveling 2100 fps with 636 lb. lbs of energy, there really isn't a lot of "recoil" at all, but there is quite a bit of muzzle blast which shakes and flips the muzzle, but it's very manageable, and depending on the combination of recoil and muzzle blast, easier to manage than most .40 S&W rounds.
The first time I shot this bullet I couldn't believe how little perceived recoil there was. Although the diameter of .40 S&W does not lend itself to 65 grain bullets, Underwood does have 100 and 115 grain offerings. I'd be interested to know how these measure up against heavier +P 9mm rounds. We may find there is some overlap in .40 S&W and 9mm. My guess is that a 147 grain +P or +p+ 9mm round, for example, would have more "recoil" than a standard pressure 100 grain .40 S&W round, but with less energy.
The weight of the pistol obviously makes a big difference. I had read that the Secret Service actually wanted to stay with .357 SIG, but when they tested the Glock 31, 32, and 33, the Glock platform didn't handle recoil as well as their SIG P229s despite having a lower bore axis and greater grip angle (which mitigates recoil by forcing the shooter to cant their wrist to line up the sights), but because they were committed [for whatever reason] to switch to Glock, they went with 9mm. I owned a Glock 33 and I own a SIG P229 chambered in .357 SIG. That's not too terribly fair a comparison, but I did use a full size grip on the G33, and there is not much of a difference between the length of slides as you might imagine, and there is no question that the SIG handles the recoil much better because of the additional weight. Glocks chambered in .357 SIG are certainly manageable for many, but certainly not for everyone, but in my opinion, literally anyone can shoot a 65 grain .357 SIG bullet from a P229, and it's a more powerful load than anything I am aware of offered in 9mm, .40 S&W, or .45 ACP. You have to go to 10mm before you get more powerful, but even then, this .357 SIG round meets or exceeds most 10mm offerings (certainly beating Hornady Critical Duty, Speed Gold Dot, Federal HST, etc.).