The entire thing is a bug-a-boo based on incorrect assumptions blown all out of proportion, and claims of danger where there is none, or would be none if proper procedures are followed.
The first incorrect assumption is the idea that you should be able to shoot your gun with anything, forever, without needing to clean it. (and clean it correctly)
The next false assumption is that any chamber overpressure (above listed operating specs) will blow up a gun. It won't, unless your gun is seriously defective.
The most commonly mentioned example is the "crud ring" from shooting .38s in a .357 chamber preventing the chambering of the longer .357 ammo.
It is true, this can happen. Now ask the guys worried about it how many rounds it will take for this to happen.
They won't tell you. They CAN'T tell you. No one knows, there is NO hard and fast number. It all depends on the gun and the specific ammo being shot.
It's possible it could happen after a few rounds. Not likely but not impossible. It might not happen until after a few hundred rounds. And, even if it does, all that means is that you didn't clean your gun soon enough. That's a failure of the user, not the gun or the ammo.
A tight fitting brush, the proper solvents and some effort, done at the right time is all that is needed to clean the fouling out. A regular bore size brush often is not oversized enough, and a larger one may be needed.
If it takes a reamer to remove the fouling
you waited WAAAY too long before cleaning.
I will not speak to the accuracy issues faced by match shooters, they may have a point, I don't know, I don't do what they do, or use what they use.
Literally the "problem" is caused by not properly cleaning the gun at the necessary intervals based on what you are shooting. This is a user error, not a gun or ammo flaw.
Ask the guys shooting muzzle loaders and black powder, or the guys shooting black powder cartridge guns, how many rounds can they shoot before they NEED to clean their guns because of fouling?
Same basic principle, all that differs is the degree. You must remove the crud build up or the gun will stop working properly, and in extreme cases, work at all.