Comment by mpyne

In fact Qt was speed up noticeably for most use cases by their 'raster' graphics engine instead of the native X11 one.

Some of that is due to the X11 engine not being optimal, but then again if it's difficult to generate an optimal X11 rendering toolkit and it's easy to make a fast software renderer, then maybe that makes choices like these (moving to software-everything) seem more reasonable in retrospect.