Yes, I will enter the fray here with some comments about a few of these "techniques".
Riding the slide is never a good idea. I cannot think of one manufacturer who recommends this and can probably say with confidence that virtually no qualified and knowledgeable instructor would tell someone to do this. In fact, one manufacturer tells you right in their owner's manuals NOT to do something like this. Kahr recommends chambering the first round from a held back and fixed slide which is then just allowed to slam closed into battery.
Bullet setback is not likely to result in over pressure loads as one might think. I handloaded ammunition for over 30 years and in magnum handgun loads, the powder fills the case right up to the base of the bullet (yes, powder for magnum loads is slower burning than for non-magnum loads). A primary concern with bullet setback is failure to feed or jamming. So yes you should rotate your rounds and not chamber the same round all the time.
As for carrying a sidearm with a round in the chamber, most definitely you should do this but only when you have trained enough and are comfortable enough to do this safely for yourself and others. The amount of time expended in a crisis situation can be very small and may not leave you with enough of it to chamber a round in order to get your piece into full battery. Carrying it with one in the pipe is the preferred method.
All I know is this:
1. I have never had any bullet setback.
2. I know for a fact that my carry gun is 100% in full battery, ready to fire after loading.
3. No abnormal wear, breakage, or weakening of the extractor has been seen.
4. Whether the cause is overpressure from bullet setback, or weakening of neck tension in the round causing the bullet to obstruct the barrel, bullet setback can be a very serious condition:
I have developed a method of loading my gun and performing redundant checks to ensure with 100% confidence a gun that is in full battery with a properly functioning extractor, a full magazine +1 chambered that reduces the chances of bullet setback to the lowest possible level. Yes, you are correct that the manufacturer does not recommend my method. However, if you followed every manufacturer's caution and recommendation to the letter, shooters would not shoot reloads through about half the pistols manufactured because there are cautions in the owner's manuals, and in some cases statements of voided warranties in the manuals, from using reloaded ammunition.
Also, btw, when I do instruct new shooters at the range, one of the statements that I make is that motions made when handling the firearm should be made firmly and forcefully. Don't baby the gun, it is made of very strong steel and polymer. The gun is designed and manufactured to handle the forces created from firing, you're not going to break the gun by releasing the slide or slapping the magazine forcefully to ensure full insertion. Under range conditions, where new ammo is loaded and used, I would correct someone for riding the slide as an improper method of loading.
However, under the condition of preserving the quality of carry ammunition and performing redundant second checks to ensure proper loading of the gun, my method has worked for me 100% of the time and I have no issues with rounds getting shorter over time.