In the event of a social breakdown, all bets are off. However, during relatively ‘normal’ times,in the USA, most armed encounters by civilians end without a shot fired. Most perps simply don’t like the idea of being shot. They are people of low moral character, bullies, and not that brave when facing someone who can kill them.
In the encounters where shots are fired, it’s typically 7m or less and the average number of rounds fired is two. Multiple perpetrators occur in about 1 in every 3 such encounters, and typically when one perp is shot, the others almost always flee the scene, seldom trying to rescue their buddy if he’s down and immobile.
It’s been my observation that in the USA, many perps who will pull a weapon on a civilian and attack them will think twice about doing that to a cop. A perp who will fire at a cop is an extra level of desperate, crazy, or suicidal. A civilian, typically the perp doesn’t know whether they are armed or not. A cop they know he or she is armed, and one yell into the radio away from backup.
Few perps wear body armor and when you get right down to it, any handgun is way better than no handgun. Even a .22 rimfire when used in defensive shootings, has shown itself to have a 34% fatality rate per shot.
Whatever weapon the person carries, they have to shoot it well. Shot placement matters a lot more than caliber. Three rapid shots in the chest with a .22LR is a lot more effective than a miss with a .44mag. Think about the difference between facing Woody Allen with a .44mag vs facing Clint Eastwood with a .22LR Beretta Bobcat.
Really, though, it boils down to a personal choice. This is a metal and plastic object that a person wears all of the time. They have to like it and be comfortable with it or it will start getting left at home or in the car too much. That is bad because it has to be with you to be effective. In all truth, choosing a CCW handgun is a lot like choosing your preferred style of underwear. It’s a choice that in the end only the wearer can make if they want the best fit and what they like the most.