I agree with you, Rob.
I took a class with an ER surgeon who is an active shooter. He's an LFI affiliate who teaches "Tactical Anatomy"--he studies this stuff. According to him, there is no discernible difference between any of the service calibers in terms of the wound or terminal effect. If they hit the T-Spine, they stay in, otherwise even the hollow points of any caliber, will likely go out. He viewed that as a good thing in terms of the wounding potential.
There are big differences on paper between 9, 40, and 45, but in real situations there just isn't one that is recognizable when using modern defensive ammo.
That said--if someone told you that they would pass a rebar through your chest cavity but you got to choose between 3/8" and 3/4", most of us would take 3/8". Practical difference? not much. But bigger wounds are bigger wounds! It may be academic, but if that extra 2.43mm of bullet diameter is enough to enhance your confidence, I'm all for it.
Dan