Two words.
Shot Placement.
Caliber is irrelevant, number of rounds a gun holds is irrelevant, shot placement is critical.
A .22 single shot is plenty of gun, IF the shot can be placed properly.
Our Nevada CCW instruction stresses that no one needs to be able to hit an assailant beyond 25 feet!
I practice to 50 yards.
If I am up against someone with a semi-automatic rifle and I have a 5 shot revolver, I am “out-gunned” and running for cover.