First, the .45 auto is one of the most accurate of sidearms.
Second, firearms kill by inflicting trauma on the target.
Third, the .357 magnum, the .45 ACO , the .40S&W, and the 9mm can all do the job as a defensive sidearm. I do not dicount the .38 spl in as useful nor the .380 acp. People can be dropped with a well place .22 cal short (but I do not like to bet on those probablities).
Fourth, there are many factors that can go into selection of pistol/caliber including concealability, weight, number of rounds, carry situation.
Fifth, shot placement beats caliber every time. A .50 cal AE in the floor is nowhere near as likely to stop an attack as a .22 short lodged in the medula oblongata after entering through the occular socket.
The reason they make so many different sidearms is that people have different hands arms muscle development and tolerance of recoil.
I know you already knew this I just had to state these facts once more.
Stay well - Stay safe - Stay armed - Yorktown