If you shoot a moose, bear, buck, I really don't care what; and place a bad shot, a 338 won't take him down. On the other hand, a 270 will drop a black bear perfectly fine if you hit him right. With “hand guns” and in the low velocity ranges you have an excellent point. The 45 has a lot more target effect than say a 9mm, but in the realm of high velocity, things change. -IMHO
A firefight is a lot different from hunting elk. Proper shot placement isn't always an option in a firefight at night at 300 meters with iron sights. Especially when the target is hiding behind rocks and shooting back. In that case I want the biggest, badest bullet traveling at the highest velocity to create a huge wound cavity and immediate incapacitation. When I hit someone I want them to stop shooting at me immediately, not ten minutes from now.