Given this data and my experience in both law enforcement and as an instructor, I’d argue that the better results in police qualifiers with 9mm isn’t due to an inherent advantage of the caliber. The sad truth is that the average cop doesn’t have nearly as much training as people think. There are many, many officers who barely pass, and their shooting fundamentals aren’t very solid.
Recoil doesn’t create problems with shooting. It only amplifies them. If you suck and can barely pass an easy shooting test with 9mm, you can’t blame recoil from .40 S&W or .45 ACP ammo for your problems. In most cases, it’s probably that you need better fundamentals — better grip, better stance, and better trigger control — assuming you’re not a five-foot-nothing 98-pounder or don’t have problems with age or disability, of course.
Like clothing, vehicles, and just about anything else in life, you have to go with what fits the situation. The truth is that you should probably choose the most powerful caliber you can shoot well that also fits your defensive and carry/concealment needs.
That can and sometimes does change over time as you gain skill or lose ability with age. It could also vary depending on what situations you’re carrying into on particular day. So in the end, even an individual may not be able to settle on just one caliber that works for them in