The FBI report has some pretty scary assumptions.
First off, let me say I'm finally (don't laugh it's been hard or me) not going to get so`much into the caliber debate as what the report says. 9mm is adequate for a personal sidearm. The .45 gives more power and believe it or not the .40 gives more. But, in looking at the big picture, the extra power may not be needed and could also end up as a detriment. It's not so much my opinion as the reports findings.
A good video on this was posted by Papa zero three. The video was of the head trauma surgeon at a major city hospital. The medical cross section of numerous .40, 9mm and .45 cal hits is that none of the rounds really causes "stopping power". They penetrate in general order of .40, .45 and 9mm. .40 is in front of .45 probably because of velocity. The thing that makes any of them deadly is the ability to hit center mass and open up a large blood vessel or organ. None of the rounds move fast enough to inflict "hydraulic shock", the truly deadly phenomenon that smashes cells and organs internally by large energy transference. Which leads to massive loss of blood. In most cases that is why a gunshot victim dies. The only reason the .45 would be a better choice is it's wider and has a larger expansion capability. Barely enough to even notice in the scheme of things.
My problem with their report is two things. First, that FBI agents who "don't remain proficient" are far more likely to be able to keep their pistol aimed 'center-mass'. Second, is the report states "bigger calibers are wearing out the service issue guns" too fast.
So, my isssue with the first point is, "Why are FBI/Gov. LE agents being allowed to let their skills degrade to the point that all they can shoot is a 9mm? That is not an excuse to move to a lesser caliber, even if it is sufficient. Because sooner or later, they (FBI/Gov LE agencies) will be saying the .380 is okay and the .38 special worked just fine.
To the second point, since when have all these larger caliber guns worn out? We had tons of WWII issue .45's when I was in. A lot of them saw service in Viet Nam. We shot them a lot and didn't see too many break. The report goes on to say all the SOF units can't keep up with replacement parts for the .45's because they wear out so fast. LE departments across the nation are seeing excessive wear on department issue handguns as the larger calibers just break them down. This doesn't make a whole lot of sense to me as I know of older Glocks and polymer pistols that have been shooting .40 and .45 for years.
While the report simplifies that the 9mm is adequate for everyone, I will continue to prefer my .40 and .45