The problem with the PGTK frontend is it is notoriously EXTREMELY slow. The latency on user input compared to the X11 (especially Lucid) version has some people reverting back to X11/Lucid.

When I do run Linux I run Wayland, I daily drive macOS, but better than both are what you already allude to: the Emacs widget toolkit which will focus on replacing the GUI frontend with SDL and also (equally potentially) introducing an actor-type framework (akin to BEAM's) for communication to decouple that GUI.

It's not just slow, it's also broken.

Maybe broken is the wrong word, but it handles chained chords differently and it breaks my workflow at least.

(C-s s C-s for instance needs you to release and press S again when lucid doesn't need it)