We have in fact created a dedicated site for people to report UX issues, provide feedback, and discuss solutions that we then implement as we're able: https://gitlab.gnome.org/Teams/GIMP/Design/gimp-ux/-/work_items
We also now have a dedicated "UX/UI Improvements" section in our release post to promote this effort and highlight work by designers.
I won't say it's perfect, but I think we're gradually convincing people we want to improve in that area, and welcome their help.