Even moving windows appears to stutter in Gnome Shell, but the minimize animation shows the real difference. On Gnome Shell, it looks like it's limited to 15 fps on RGB windows, while on RGBA windows (these with GTK Headerbar for example), it animates so slowly that I can count every frame. Also in Wayland mode, the cursor stutters or even freezes when animation is being rendered.
On Mutter however, everything is smooth, in both, X11 and Wayland/DRM modes, cursor also works flawlessly on Wayland, and
glxgears, though reporting the same FPS as on Gnome Shell, appears to be smoother.
What can be the reason of this behavior? Doesn't all Gnome Shell should do is just draw the top bar and let Mutter handle everything else?
I'm using Gnome 3.14 on Fedora 21.