[JohnKSa]

That said, I've rechambered the same round from slide lock multiple times. I've never seen significant setback, or even visually discernible setback.

Depends on the gun and the ammo. I've seen some factory ammo that would set back very noticeably in one particular gun from a single chambering. It's something to be aware of because it can be a fairly serious issue--just not with every single gun-ammo combination out there.

...you don't really risk a malfunction if you ride the slide and make a point of riding it all the way in.

If you're careful how you do it, it's possible to make sure the gun is fully into battery. But it can cause a failure to go fully into battery which would definitely be a malfunction--and potentially a dangerous one in some guns and under some circumstances.

It seems to me that it is most common in .40, which I don't shoot, or make.

.40 is probably one reason that so many people know about setback. That's not because it's more likely to set back than any other caliber out there, but rather because there was one common loading that was very sensitive to setback. A relatively small amount of setback in that loading would cause the discharge pressure to essentially double.

Surely you have at least seen photos of pistol ammo with set back.

Yup, seen it in person, even. But I've never seen it with premium self-defense ammo that has only been chambered a few times. Chambering a round a single time shouldn't raise any concerns about setback. If that weren't true, semi-auto pistols would be dangerous to shoot normally.

Chambering good quality self-defense ammo 4-5 times or less, shouldn't be an issue either, but it never hurts to do some checking on your own to see how your particular gun/ammo combination behaves.

Anyway, all that to say that concerns about setback should be addressed by using different ammunition, or by limiting the number of times a given round is chambered, not by coming up with non-standard operating procedures for the pistol.