There is training to use best tactics and strategies, and, there is the training to use the weapon(s) well. The former can be very important, even for those who do not have a favored weapon available, or, any actual firearm at all, when the real-world critical incident happens. The tactics and strategy training is the most important, in my opinion.
Then, there is the weapon, itself, and the training to use the weapon well. As I see it, these are co-equal.
Ultimately, there is the wisdom of training that combines all of the above.
On the matter of choosing a single-action revolving pistol, versus a more modern weapon system, well, a modern weapon can offer more options to the user, while requiring less manipulation. In the typical face-to-face armed robbery, I see no disadvantage in being armed with a single-action revolving pistol, if the defender is comfortable AND skilled using the ol’ sixgun for quick and accurate hits. Five or six is enough, until it isn’t. If that five or six are not enough, well, ten to seventeen may fall short, too.
Two times in my life, I have found SAA-pattern single action sixguns to be desirable for defensive purposes. The first time was a couple of decades ago, or so, when I had so sleep with “carpal tunnel” splints on BOTH of my wrists, while sleeping. I found that the one weapon which worked well, if I had to shoot, while wearing the splints, was a USFA Single Action, that became my bedside companion. I carried my SIG P229 while on duty, when I was not wearing the splints. I probably carried a pair of Ruger SP101 snub-guns, during personal time. If not, it was a P229. The next time I found SAA-pattern sixguns to be viable for defensive use, started last year, and continues to the present. Arthritis moving into the second knuckles of BOTH of my index fingers effectively ended 40+ years of long-stroke double-action trigger pulling, with medium-frame* revolvers. This also ended training with most types of DA autos. Well, if I have to cock a hammer, anyway, to shoot a revolver in single-action mode, it is more expedient to use a single-action sixgun, with a hammer that is situated and shaped to facilitate thumb-cocking. A different problem can affect my ability to use my right hand to run an auto-pistol's slide, when shooting lefty, and to provide a firm-enough support to the frame while shooting righty. My days of using auto-loaders being potentially limited, it is a best practice for me to train with my SA sixguns.
Tom Givens, founder of Rangemaster, and a member of this forum, has made a diligent effort to follow-up on the shooting incidents that have involved his students. If I recall correctly, he arrived at a comfortable minimum ammo capacity, by studying how many rounds his students needed to successfully prevail. I would rather not put words into anyone’s mouth, or guess, and be wrong, but I am reasonably certain that the number was not fifteen or seventeen. I remember being comfortable with two five-shot revolvers, based upon what he wrote.
*At least for the present time, I am still able to shoot SP101 and J-Frame revolvers in DA mode, due to the differing dimensions resulting in differing finger positions, which means less stress concentrated on the second knuckle of each trigger finger.