In other words, a .45 ACP works best when fired from a .45 automatic.
While perhaps you can't count on stopping someone with one shot, you also can't guarantee hitting your adversary with all shots fired, either. So both the absolute and relative effectiveness of the bulllet is important. There's more.
While some may believe the .45 ACP is anemic, the problem of more powerful cartridges, including all the magnums, the 10mm, the .40, and perhaps the .357 Sig, is both shootability and controlability, and that also applies to the .45 ACP fired from small and lightweight handguns. They can all be a handful to shoot, even more so the lighter the gun is, and the blast from some of them can be something else. That all translates to slower follow-up shots, unless you think that isn't important, although it remains true. Naturally, all that varies from individual to individual. Some will think a 45-ounce .44 magnum revolver is a nice all-round handgun, also suitable for concealed carry. But that person may expect to jump a bear or lion on the way to the outhouse. Others may have other concerns that weigh heavier.