I Suppose it is a blanket statement, but I will stick with it anyway. AND! You are correct in saying certain areas concerning the 45acp verses the 9mm. EXAMPLE: 45acp ball many times will not penetrate car wind shields, and 9mm ball most times will. However! 45acp ball ammo will expend far more energy INSIDE a perp than 9mm ball will, which usually will zip on thru. 45acp will more often break bone, while 9mm will more often glance off bone, both dependant on bullet configuration.
In 1977 I used a 357 magnum to stop a situation where a car was cover. The 357 magnum performed fairly well. In June of 1978, a similar situation where a car was cover, and the 45acp I was carrying failed miserably, but I still finished first.
As a whole thru my PERSONAL experience these are the boundaries I have came to accept for MYSELF, and as you said it is somewhat of a blanket statement, but I will hang with it, as thru my own experience, and that of other officers I personally questioned, I am comfortable with my decision on minimum caliber. It is all dependent on the individual, and their own decision.
The most important decision is before someone carrys, will they, and can they emotionally, stand and fight. Many claim they can, but can't, and most claim they can, and don't really know. In 1966, a friend of mine stood at the front fender of a patrol car, while a black panther member stood at the opposite side fender, and they shot it out across the car hood, with the perp getting the first shot off. Their guns were less than 3 feet apart. No one quit until the perp took a 357 mag round to the chin. By the way, the perp was armed with a 1911 that was working very well, but not well enough to beat the six shooter. That friend also won another fight with the same wheel gun in 1979 against a sawed off shotgun. That perp also got the first round off. Both of these fights occurred late at night, and there were not night sights, or laser back then. It was difficult conditions, and a don't quit attitude that won both fights. How many have the grit to stand and fight a guy like my friend? There are perps that have that much grit, and once it starts it has to be finished. Folks need to consider that, as sometimes pulling a gun escalates the situation, rather than deterring it.
There are many considerations beyond caliber, and platform, such as temperament.