Agree that it does make the product better, though if they put their RAM chips soldered on the board instead of in package, it would allow repair or upgrade without sacrificing the whole CPU unit.

GPUs do not put their RAM in the same package as the processor itself, and it does not sacrifice a significant amount of performance.

The M-series processors' primary benefit by a huge margin is its architecture that allows a higher memory bandwidth than say SODIMMs and that benefit is independent of the choice to put the RAM in the package.

I think when they moved to the M series they had trouble providing enough PCIe lanes. Not that I ever really trust Apple to ever offer non-proprietary storage again, but moving the storage controller to the SoC probably avoids any PCIe support they'd have to think about.