You call the emphasis on shot placement 'arrogance' yet the majority of people who have actually been in gunfights point to this, not capacity or bullet size, as the reason they survived.
I can think of a number of instances where this concept has been considered to have some merit.
Capacity will never take the place of professional training and constant practice (combined with situational awareness.)
I agree, and would include caliber considerations to a reasonable degree, as well.
For example, during some recent training I had the chance to listen to some cops discuss shooting situations in which they had been seriously wounded.
One of them involved a situation which had been recorded on an open line, involving 3 cops and 1 armed suspect. As I remember, a total of 31 rounds were fired within just 10 seconds by the time the shooting was over. The cop who ended the incident had received several serious gunshot wounds, as had the suspect. He said when he was laying on the ground seriously injured he took the time to aim at the suspect's head and fired until the suspect stopped shooting. I think I remember that it was determined that he made 3 rapid and accurately placed head shots to end the fight (I'd have to check my notes). He was shooting a 9mm.
Another cop took us through his shooting incident in which he exchanged shots with an armed suspect from relatively close range (5 feet) to as far as 100 feet, if I remember right (I'd have to again check my notes). He said that it wasn't until he realized that he was on his last magazine, was seriously wounded and the suspect was still shooting at him, that he said he realized he had to stop shooting 'instinctively' and settle down to use his sights. He fired 2 rounds (shots 22 & 23, I seem to recall) which hit the suspect and stopped the fight long enough for help to arrive. The cop was shooting a .40 S&W.
Another cop took a hit through the lower part of the heart from a .357 Magnum revolver at close range, but managed to fire 4 rounds from an issued 9mm and stop the attacker (killing him), before succumbing to the life-threatening injury which required extensive surgery and recovery time. The cop credits being able to effectively use the shooting skills received in training and which she had practiced a lot.
I remember watching a tape during a lecture where a cop known as a fine marksman during training was only able to make 1 hit on an armed attacker during a shooting incident resulting from a vehicle stop. Stress can have adverse affects, especially when it's the result of hormonally induced (fear) and not only the result of physical exertion.
I've spoken to a number of other cops who have been involved in shooting situations, a number of whom I've worked with on the range.
I can only remember a couple of them mentioning any preference for caliber.
One of them was involved in an off-duty shooting with an unknown (fled) suspect who had apparently been armed with a 9mm pistol, while the off-duty gentleman had only been armed with a .25 ACP. The distance involved in the shooting was farther than that typically reported, described as across a city street. The off-duty cop wasn't wounded and it was unknown if the suspect who fled had been wounded, but the cop immediately got himself a larger off-duty weapon. He seemed to take his sessions at the range a bit more seriously, too.
While calibers, ammunition, guns and situations have varied among the cops and civilians I've known who have used handguns to defend themselves, a couple of things which seem to have remained consistent is that handgun wounds which have hit and penetrated into critical parts of the anatomy have seemingly been more effective than rounds which hit less critical anatomical structures, organs and tissues, as well as rounds which entirely missed the target.
Skillset is important. Mindset is important. Proper, realistic training can help with both. Sufficiently frequent practice is important. Shooting is a perishable skill.
Oh yeah. Once time we invited a couple of guys from the local shooting club to participate in some simple qualification drills. I know one of the guys is a very skilled, experienced and accomplish competitive shooter who has enjoyed success at Camp Perry pistol shooting. Once he put on a gun belt and holster, though, and was facing a silhouette target instead of a bulls-eye target, he was pretty dismayed to find out that he experienced a different type of stress and delivered a rather basket-ball sized group at fairly close range.
This isn't the first time I've had the opportunity to see something along this line, either.
It was much the same in the martial arts. Some folks do well in non-confrontational training. A smaller number do well in limited contact competitions. A smaller number do well in more challenging competitive conditions involving more physical contact. And even a smaller number seem able to rise to the challenge of effectively utilizing their skills when faced with an actual attacker in an unexpected situation. Dunno. Just my thoughts.
I'd hope that most folks wouldn't mistakenly overlook the importance of mindset, training, skillset and sufficiently frequent practice to maintain skills under stressful conditions, in favor of placing what might turn out to be an unfortunately misplaced amount of confidence in any particular caliber or weapon capacity.
I still remember the last time I was specifically fired upon. It happened when I was in my car, involving a person, or persons, unknown. It really didn't matter what gun I was carrying at the time since I wasn't in a position to be able to locate and identify my attacker(s?), let alone effectively employ my handgun. I DA'd the area after the second round hit the window behind me and reported it to the locals. They weren't all that surprised, and I later found out I wasn't the only victim who had made a report. This was probably 20 years ago.