What i did more than once was directly get in contact with a mantainer or the lead developer(more often than not i befriended them too) and suggest some GUI improvements directly, it's ofc not doable everytime because otherwise the devs would just have too many people to manage.
Instead, ask if you can join the development team as the "UX/UI person" and show what works you already did, there is a good chance that you can either join or they will ear you out more often when you make an Issue/PR

Yeah, I think the extension of "We need to acknowledge that UX is important" is going to be "We need to negotiate a mode of working that enables UX volunteers to help efficiently." I've been out of software development for years, only tangentially worked with UX designers for a university project (and even that was basically just a bunch of UI mockups I was supposed to implement, so I never saw the process). I don't know how the industry has solved that question (if at all), but the less hierarchical FOSS system may have to find its own way.

I'm glad that you have any interest in the topic at all, and thank you for shedding some light on your side of the issue.