Hogwash. Yes, 9mm is more effective that it used to be because of improvements in bullets, powder, etc. Those same improvements were also made to the .40S&W cartridge. Do people think that .40 S&W ammo today is the same as it was in 1991? The ONLY reason that LEO agencies are switching back to 9mm is cost. Money is the overwhelming factor for the switch. It is a myth that 9mm is just as effective as .40S&W.
Cost is a factor, but it is far from the, "only reason". It is one of many. The .40 S&W was a solution to a non existent problem, period. .055 increase in bullet diameter does not make it a wonder cartridge. Especially with today's modern expanding self defense ammunition. It makes it what it is..... A "10 MM Special", nothing more.
Even more anemic than the pathetic, "FBI 10 MM Load" Federal concocted for them, that started the whole run away train that led to the .40 S&W in the first place. It's only accomplishment was to generate more recoil in 9 MM frame guns that tears them up faster. It is NOT difficult to shoot. Especially in full sized duty weapons.
So, where does that leave it?
1.) The ammunition costs more.
2.) It has NOT proven to be any more measurably effective, in hundreds of law enforcement analyzed shootings.
3.) It tears up guns faster resulting in a shorter service life.
4.) Pistols chambered for it hold less ammunition than comparable 9 MM weapons.
ALL of these factors have been PROVEN, and are NOT opinion or speculation. It doesn't take a rocket scientist to understand why the .40 is going down, while the 9 MM is going up. Everything else is nothing but a bunch of Saturday afternoon bar stool crap.