The specific thing I noticed was that, when pressing alt-tab the very first time, there was a noticeable, variable delay for the actual window previews to appear. I don't care as much about the window previews, but the delay in feedback to know which window I was potentially focusing on was painful. I also alt-tab like a madman, for better or for worse. Testing this now on Windows, after I press tab there is an _immediate_ rendering of the previews, 0 (noticeable) delay. On KDE, I'm not exaggerating, I could count 1-2 seconds until I saw something on screen, even when my machine was mostly idle (Discord+music player running).