> AFAIK, the only Linux desktop environments that come close are GNOME and Unity.

I'm the project lead of LXQt. All those things you listed can be supported without introducing much bloat at all. In DEs, most bloat comes from pure technical debt. Unnecessary libraries, duplicated code/libs, etc.

Feature bloat is another matter and is more subjective. A lot of it is down to UX.

Fun fact: KDE 4.x depends on ruby in most distros. Do you know why? Dolphin ships with a ruby script to update some folders (don't remember what it does). Nobody runs it. That's it.