Nevertheless, what usually happens is people buy a double-action and use it almost exclusively as a single-action, never learning to use effectively.
I think I know what you mean, but I disagree with the wording of the statement. Being able to shoot it well in both single action, and double action is the most
efficient way to fully use a DA revolver. Shooting it SA might not be as efficient, but it is certainly
effective.
When I was growing up, my Dad had half a dozen handguns. More than anyone else in our little town. Friend up the road had two, a much more common situation in our locality. So, I was in fat city, in that regard.
Dad, however, did not own a single action revolver. He didn't care for the grip shape. I got to learn on DA revolvers (shot almost exclusively SA), and autopistols. With two exceptions. Mom had a Ruger Super Bearcat. This was a neat gun, and lots of fun, but it was a little too small for me by the time I reached teenage years. Mom was a small woman (size 3.5 ring) and it fitted her perfectly.
My other experience with a single action was our friend up the road who had a Ruger Blackhawk in .357 Mag. Yes, I watched cowboy shows and played as a kid, but I never "fell for" the single action because it was the cowboy gun. For me, it was just another kind of revolver, nice, but nothing special.
A couple years after finishing my world tour with Uncle Sam, I was in a position to get a handgun of my own. I got a .45 auto. One of the early Sig P220s, imported by Browning. Sweet gun, still have it.
A couple years after that, I found a Ruger new model Blackhawk convertible, in .45 caliber (7.5" barrel). At the time, I though, this is neat, I can plink with my .45 auto ammo, and not have to dig in the weeds to find my brass to reload!
I made one small mistake. On my way home with the gun, I figured I might as well have some ammo for its "other" caliber, so I stopped and got a box of Winchester .45 Colt. My "mistake" was shooting some of that ammo, first.
WOW! OH MY Goodness! IT was FUN!!!!!! The roar, the muzzle flip, cranking back the hammer for the next shot! It was FREAKING GREAT!!!!
I was hooked! on both the .45 Colt, and the Ruger Blackhawk. In a bit over 30 years that I have had that gun, I have shot, maybe 300 rnds of .45ACP through it. Several thousand .45 Colt loads have gone downrange though, from mild to wild.
The single action revolver, particularly the modern designs like the new model Ruger are efficient and effective firearms, and particularly in the larger calibers are smaller and lighter (slightly) than DA revolvers, even with the same barrel lengths.
The feel of the grip is completely different. The balance is different. The whole cowboy/nostalgia thing for the SA is lost on me, but its a BIG thing for a lot of people. No, they aren't as efficient for combat as more modern style guns. And most consider them not as good for personal defense as a DA gun (note I make a distinction between defense and combat). But some still use them for that, and they are every bit as good today as they were in the 1870s, and some models are mechanically better.
I got involved in shooting in an era when outside of those with police training, and a handful of experts, virtually everyone I knew or met considered the DA feature of a DA revolver to be an "emergency use only" option.
Things, particularly general opinion have changed a lot since then, but some things are still the same. Those with a desire can, and do master DA shooting. Those without, will shoot their DA guns SA, 99% of the time.
I don't, personally, care for the Colt Single Action revolver. I know they are the Holy Grail for a lot of SA shooters, but not for me. After over 30 years of using Ruger Blackhawks (new model) in various versions, the Colt and its clones seems small, frail, and weak to me. I know they aren't, but the impression persists. After decades using S&W N frames, I feel the same way about K frames, too!
It a personal thing.