You are correct that it does, but not every change made by engineers is a UX change. But even if you want to think of it like that, the backend changes still need to happen first in order to get any significant UX change going.

>small developer led teams often refuse to bother to even consider that they have to change anything to fix these things.

The GIMP developers are aware of this pitfall and want to avoid it, there is even a FAQ entry about it: https://www.gimp.org/docs/userfaq.html#i-dont-like-gimps-use...