The guy I hear keep repeating this is John Corriea from ASP. He does always stress "MOST" end in less than 5 rounds......not all and he does not suggest carrying 5 bullets.And this is why the 3-5 average saying (with no one even providing the study that gave those numbers) is fudd lore and imho dangerous to keep telling new and ignorant (for lack of better terms) tun owners.
It gives people a false sense of security.. oh i only need a 7 round glock 43 because... or we can't have 30 round magazines, that's ok 10 will get the job done with extras left over
He just says a 5 round snubbie is better than nothing.