I notice he disallows 'larger' as an option early:
You have two options. You can use a really large round at very high velocity like the 30mm cannon rounds from an Apache helicopter's M230 Chain Gun, which produces substantial kinetic energy, or you can place your shot where it has the most effect. Obviously, shot placement is the only realistic option for a law enforcement officer.Well, if that's obvious, we're done. Lower recoil is more important than size. But that doesn't follow all the way down: .22 LR is a terrible choice, although recoil is minimized to the point that it is almost negligible.
For myself, I favor .44-.45 diameter choices. I realize that the science shows that .357 Magnum out of a four inch barrel is the best one-shot stopper. I favor .44 Smith & Wesson Special or properly structured .44 Remington Magnum or .45 Long Colt cartridges for revolvers. These have the advantage that, when hiking in grizzly and moose country, you can readily step up to a cartridge that can handle big game defensively.
As a consequence, if I carry a semi-automatic, I prefer .45 ACP as the closest equivalent to .44 SPL. Still, if the suggestion is that there's no difference in trauma worth noting between .40 S&W and 9mm, the lower recoil could be decisive.