Per Lucky Gunner tests:
- 9mm 124gr +P HST expands to 0.66" diameter. That's an area of 0.3421"
- .45acp 230gr HST expands to 0.85" diameter. That's an area of 0.5675"
I fail to see how a hole that's 65% larger isn't objectively better. No, it's not a death ray or a rifle round or anything but a bigger hole should cause faster blood loss and have a slightly higher chance of nicking a major organ or part of the CNS.
I'll say again: that's the only advantage of the .45acp - everything else goes to the 9mm to some degree.