What we have here is a failure to learn history. Why was the .45 adopted in the first place. The .45 was adopted due the the Army .38 revolvers’ abysmal failure to put down Moslem insurrectionists who were whacked to the eyeballs in the Phillipines in 1902. In Iraq, post-mortems in Iraqi insurrectionists revealed that these men were doped to the eyeballs and that the 9mm and, for that matter, the 5.56mm rounds were marginal at best for bbringing them down.
Especially in its military hard-ball form, the 9mm is NOT a reliable man-stopper.
Back when the switch was made (during the Cold War), having good penetration against Warsaw Pact body armor was a reasonable enough concern.
It should also be noted that the .45 ACP was designed to approximate the ballistics of the .45 Colt.