> If you install linageOS, the picture quality of the camera apparently falls dramatically, so the software does something better than stock.

Drivers are another matter. But vendor replacement apps seem almost universally worse than the stock versions.

I can't speak about Samsung, but the Moto G4 Plus also suffers from the same limitation, that the stock camera app can't use the hardware's unique features. But there are ways to overcome that. It's pretty easy to find deodex ROMs for just the camera apps. That way, we can run the manufacturers' apps even if they have crippled their software to run on only their ROMs.

I thought it's because they don't release the blobs/binaries for the camera. So when you another ROM, you have to use generic post-processing for the camera