In WWII we won because for every plane the axis made we made 10, same for tanks, boats, Etc. That having been said the 9mm is the only major caliber, for every 40 s&w and 45acp that are sold, 4x 9mm are sold. For every box of 45acp or 40 s&w that are sold 10x 9mm boxes are sold.
As far as slow but heavy projectiles lets go back to WWII once again. Before the war the Brits actually named their artillery by the wt of the projectile because their enfaces was on heavy and slow . But the Germans put an end to that with the 88mm FLAK, it shot a projectile as fast as was possible and nothing could stop it except being overwhelmed by numbers.
So, 9mm has the volume to overwhelm, and the best velocity, my P226 is 15+1 rounds. That give 5 two round bursts before I have to go defensive.
New York: where we import politicians but no standard cap mag.s.