Does it matter? They are after all just inanimate objects that can be replaced with better ones.
Well. I think there are some rifles I'd like have last a lifetime...
Barrels and throats are one thing, and firing factory ammo is fine, but hot loads (by definition: hotter than standard spec) will most definitely wear out a firearm -and not just the barrel. The action will eventually give way. The US Army Ordnance labs did extensive tests with this in both small arms and artillery. They found that with a steady diet of over-loaded rounds, the metallurgical changes they brought about eventually caused breech failures which were very abrupt: All was working fine and then, catastrophic failure.
Firearms are like any other mechanical device. Push it repeatedly beyond it's limits and it will give out. Their life span is finite. "Proofing" is just that: It is a proof that in worst case scenario, such as the accidental overload of a factory cartridge, a firearm will not fail. It is not a limit set for the practical,sustained strength of firearms.
Growing up around handloaders -both good and bad, and the hunting camps they frequented- there was always someone who boasted of hot loads, and how his rifle could take it in stride and how well it shot, etc., etc. It was not uncommon to eventually hear that old Joe had a blow up with his old pet rifle: blaming the powder maker, or the bullet maker or the brass... everyone but himself and his persistent hot loading of cartridges.
There used to be an axiom in handloading whereby you should load to the lowest pressures that would deliver the ballistics needed to do the job. It was prudent and economical and intelligent handloaders learned to load for efficiency. Funny how people these days largely ignore this most basic premise of handloading.~Muir