This subject can often be a thought-provoking one ... or simply a provoking one ... depending.
When we first transitioned from .357 Magnum revolvers as issued weapons (and approved calibers for personally carried service revolvers included .38 Special, .357 Magnum, .44 Special, . 41 Magnum, .44 Magnum, .45 ACP/.45 Colt revolvers) to lightweight 9mm pistols, the fellow in charge of the Firearms Training Unit advocating the change explained the basic reasons as increased fire power before reloading, faster & easier reloading, more ammunition reserve carried on the person, a lighter weapon carried on the belt and more controllability with the 9mm cartridge.
Like many other agencies, we discovered that our people's qualification scores immediately improved with the 9mm pistols, too. The .357 Magnum cartridge had always given a number of our folks some controllability problems, and 158gr LSWC +P ammunition was provided for qualification (the explanation being primarily for reasons of cost, but lesser recoil was also a result), although .357 Magnum could be used at the expense of the individual user/shooter (as if cops would spend a nickel more of their own money than was required on something like ammunition
). I switched over to training and qualification with the .357 Magnum ammunition I carried, and it was certainly expensive ... but I felt it was a worthwhile investment. I think I logged more than 3,500+ rounds of Magnum ammunition through my second 686 4" revolver by the time I turned it in on my first 9mm pistol.
If I remember right, since that time the most rounds fired in a single shooting has been 8-rounds, and the least was 2 rounds (notwithstanding the shooting of animals).
Some agencies have experienced sympathetic fire issues in some shooting situations, and having more magazine capacity can certainly add some rounds to the equation when considered against revolver capacity. Granted, that's generally considered to be a training & judgment issue ...
The ammunition capacity consideration can be debated back and forth. Smaller caliber pistols with 15-17 round magazines ... medium caliber pistols with 11-15 round magazines ... and large caliber pistols with 7-8 round magazines ... are all popular, and the number of spare magazines carried on the person seems to vary a bit, as well. That can sometimes negate the argument for 'high capacity' being a 'must-have' consideration, to some extent. When these issues aren't regulated by policy they can be subject to individual personal preference ...
Nowadays we have some 8-round .357 magnum revolvers available, and 8-round speedloaders.
The return of some all-steel weapons to L/E holsters can also affect the 'lighter weight' argument to some degree. Some all-steel L/E pistols, especially when loaded, weigh within an ounce or two of what a 686 4" revolver weighs. Then again, the extra weight can help mitigate felt recoil and enhance controllability for some folks.
The heavier revolver DA trigger stroke was always something that gave some folks problems. I remember when one of the physical agility tests was being able to rapidly cycle (dry-fire) an empty DA revolver trigger a minimum number of times within a brief time period. This test sometimes gave smaller stature, lesser strength recruits a lot of problems. The test went by the wayside with the adoption of DA/SA pistols.
The introduction of some of the newer DAO-type & SA pistol designs seems to make teaching trigger control an easier task in some respects ... and faster & easier operation of the newer, lighter trigger systems can be considered an advantage for many folks when it comes to training a lot of people. Look at all of the new pistols being released in modified DAO-type designs. (Some are really neither fish nor fowl, but you get my drift.)
Perhaps it may be a bit of a mixed blessing, though. I've always thought there's something to be said for the foundation of handgun skills developed when learning to use a DA revolver for a service weapon. Quality versus quantity ... relying more on proper grip, sight alignment/picture, trigger control and demonstrable consistent accuracy, rather than 'spray & pray', to put it one way. Training issues ...
The overall ergonomics of pistols & revolvers seems to demonstrate that more folks can be better fitted with one of the newer pistols than a revolver, since personal physical & ergonomic requirements really vary quite a bit. The difference between single & double column magazines in many pistol models can be an advantage in this respect for some folks, too ...
Faster controlled & accurately placed shots are also a potential advantage when it comes to pistols, as is recoil management & recovery when comparing pistols & revolvers chambered in powerful, defensive cartridges. Again, however, different folks have some different perceptions in these matters.
This is one of my favorite subjects for casual discussion whenever I get together with other instructors who have been in the business for enough years to have previously carried & trained with revolvers. While most everyone admits and appreciates the advantages of using a pistol instead of a revolver for L/E duties, it's often surprising how many instructors admit that they'd personally (themselves) be comfortable returning to carrying and using a revolver again ... and how many often still carry a revolver off-duty.
I have to admit, carrying an 8-shot M627 5" .357 Magnum revolver wouldn't really bother me all that much, at least for uniform usage. My uniform pistol is presently an all-steel 8+1 .45 ACP pistol.
Of course, if I carried an 8-shot revolver for uniform use I'd still really prefer something smaller for plainclothes.
It's probably safe to opine that when compared against the traditional steel revolver, the modern pistol is an overall improvement for daily L/E defensive tasks and duties ... especially when one of the newer, lighter weight models is considered, and higher capacities can be an advantage when considered from some perspectives.
In the right hands, however, I wouldn't necessarily consider a revolver user/carrier to be 'insufficiently armed'.
Remember, we're only talking about defensive handguns, after all ...
Given my choice ... and only considering handguns ... I'd rather be backed up by an experienced revolver user/shooter, even if 'only' armed with a S&W M10 .38 Spl, than a minimally proficient partner carrying some brand/model of high capacity wonder pistol which gives him/her what might charitably be called misplaced confidence in his/her abilities to actually use it, especially when under duress ...
We need to consider the overall training needs for subject like this, though.