This is something I have trouble understanding, especially for actual Glock. A guy spends the money to get a Glock, presumably to get the legendary reliability. Then he changes the barrel, slide, trigger, mag release, magazine, recoil rod and spring, and sights. I get the impression that some people make these changes before breaking in or even firing the new pistol.
Heck, might as well buy a Dagger frame and then put all the aftermarket stuff on that. Total cost would be less and reliability would be the same. I guess it’s okay to discard about 70% of the OEM parts and replace them with aftermarket if he doesn’t complain about the “improved” pistol’s reliability or accuracy.
For a pistol you’ve spent some time with, I can see making changes that you are pretty sure will help, based on your own research. If the changes are cosmetic, well go for it because it is fun. If someone is making changes because he/she believes the pistol will be more accurate or reliable, that’s tantamount to saying you know better than the people who designed it how the pistol should be configured (at least for optimum all-around performance). I know darn well that any new firearm I buy is more accurate than my shooting ability will demonstrate.
Reliability could be a genuine issue at times for oddball brands like Chiappa and similar. I had a Revelation .22 semi auto rifle years ago that was absolutely atrocious, should never have left the factory. The sights were way, way off, and It would misfeed or jam every few rounds. The rifle was nearly unusable.
The front and rear sights were half out of the dovetails to get the shooting at point of aim. Turns out the barrel was crooked, not pinned in straight. The two halves of the inner receiver parts didn’t match up right but some judicious filing and stoning got it feeding reliably.
My point is, you might be able to improve reliability and/or accuracy if the firearm obviously manifests an actual problem due to mis-manufacturing or an assembly error, and you can’t get it fixed under warranty. Trying to improve reliability before you know that’s even a problem, however, I think is oftentimes due to self-deception encouraged by overly-optimistic and possibly deliberately misleading marketing. Likewise for accuracy.