alt Hacker News> Originally, I had meant to compare with X11 sessions as well, but with KDE removing them soon, I dropped it.
Last time i checked X11 without a desktop compositor (very important) still provides the least latency of any environment, so even if KDE Plasma (not KDE as a whole AFAICT) drops support, there are other WMs/DEs that will work with it and have minimal latency on desktop.
KDE now supports the newer explicit sync (applications can signal when the frame is ready) and async presentation (fullscreen applications can tear rather than wait for the compositor frame sync). Fullscreen apps can also do direct scanout on Kwin now, and VRR is well supported. X11 w/o a compositor is of course still fewer steps for the data to pass through, but there is no longer anything uniquely available to that flow alone anymore.