This subject is rather like the "caliber debate" in that there's any number of answers, and any of them can be right, wrong or irrelevant depending on the situational context.
I often carry a 5-shot .38 Spl snub as a retirement weapon. Why? They're handy, light and convenient for those times when I don't care to belt on a large, heavier handgun. I still train, practice & qualify with them, too.
Would I carry one as a primary service weapon? Nope. But I would carry one as a secondary/backup weapon (and as an off-duty/retirement/LEOSA weapon).
I've known folks involved in shootings. The most common "realization" I've heard expressed? Aimed fire can become
very critical (regardless of available capacity, but if the
realization comes later in the shooting incident, having enough remaining capacity to start making aimed shots is a good thing).
I can think of a home invasion where one of the family members exhausted a 5-shot revolver and died.
I can think of a cop who successfully used a 5-shot revolver to stop 3 armed robbery suspects.
I can think of a cop who died holding a 5-shot revolver when intervening during an armed robbery.
I can think of many examples offered during a couple of different training classes (street tactics & LEOKA) where 5-shot revolvers successfully saved the lives of an impressive number of cops, both on & off-duty.
My thoughts on capacity have obviously been influenced by my career, including my involvement as a firearms instructor. I carried a 6-shot service revolver as a young cop, and either a 6 or 5-shot revolver off-duty, or my Colt Commander (7-rd mags back then).
I carried a variety of issued pistols over the years, starting with 14, 15 & then 12-rd 9mm's, followed by 12 & 9-rd .40's and then 8 & 7-rd .45's at the end of my career. If I were going to choose a new service weapon today, it would probably be a 9mm, in whatever capacity configuration was available at the moment. I tend to like the recoil management & controllability of the 9's ... and if it had been permitted, I'd have finished my career carrying one of my last issued 6906 12-rd guns.
Ammunition capacity can be a good thing, but it oughtn't be considered as a substitute for mindset, skillset or the proper understanding and use of awareness & tactics.
I've sometimes suspected that some folks tried (intentionally or unintentionally) to lean on "capacity" the same way they leaned on "better bullets" or bigger calibers in lieu of emphasis on personal skillsets, perseverance in training, frequency of proper practice and cultivating an optimal mindset for facing threats and potential deadly force encounters.
A rabbit's foot just takes up space in your pocket, and a handgun on the hip (or in the pocket) ought not to be a talisman.
Avoidance is a good thing, but denial isn't such a good thing.
I certainly don't have the "right" answer for any particular situation or person, and the "right" answer for me can vary from one day or anticipated situation or set of potential circumstances to the next. Probably why I still have a safe full of handguns and keep running through them on the range.
I'll offer this and stop the rambling ...
Regardless of what handgun I've carried on or off-duty (caliber or capacity) I never considered myself
well-armed, but just
armed. It was still just a handgun, after all. When I was on-duty and knew enough in advance of a serious deadly threat, the shotgun came out of the car ... (and if we'd had the right locking trunk racks for my plainclothes car before I retired, I'd have added a rifle to the shotgun I carried in the trunk).
