Some processes always run at different rates, even opposite processes, but others approach being switched (e.g. insulin/ketosis) and the mental model of switching is accurate enough for practical purposes. It's even accurate enough for practical purposes for those processes that are much more smooth and not switchy (if you are correct enough about which process dominates).

What you've said is interesting about MPS. I didn't know these things.

There is a presumption there that I want to be building muscle. This is good advice for a bodybuilder, but not so much for my case, someone trying to stay alive for as long as possible. From what I understand, the smaller I am the better, including lean mass, modulo sarcopenia.