GTK hasn't been the Gimp Toolkit in years. It's much more the GNOME Toolkit these days.
Biggest fault of the Gtk/GNOME ecosystem these days is a small bunch of atrociously toxic people centering around RedHat shouting "Nobody besides me works on this, and that! So sit tightly, and shut up with your feedback!," while completely forgetting that it was them who scared off, and trolled out most normal people out of the GNOME community, including some of the best devs they had.
>If anything, we have to turn the GNOME community around and make this community a tolerant community, and a community of love. I have to say that I am surprised by how well the gnome-love mailing list has taken of, and surprised to see various newcomers to the platform actually writing code and becoming productive.
Also, that was quite a long time ago (some posts are from earlier than 2003) and most of those people involved in those threads don't appear to be associated with the project anymore. It certainly seems like they were able to work out some of their process issues in the last 17 years seeing as how the bonobo/orbit parts were dropped entirely.
Not to say UX designer are not important, but, IMHO, very good one are rare and stubborn one common place. Not that we devs are any better.