"Bloat" doesn't mean "slow" or "memory-hungry". What "bloat" refers to is all the server-side windowing stuff that's no longer used by anything but Xaw or Motif, as well as extensions such as XRENDER that are useless nowadays. X servers carry around all of this legacy baggage that essentially goes entirely unused.
> It fails to distinguish between compositing and hardware accelerated blit operations that allow X to display multiple windows without the need for a compositor.
Compositing has been non-optional in every major desktop OS since 2006 except X. There's no point in supporting a non-compositing mode anymore, as it results in unavoidable tearing. 17 years is a long enough timespan to drop obsolete technologies.
> It talks about hardware planes but fails to mention that no Wayland compositor so far is capable of using them whereas X is using them for the mouse for a long time (which avoids mouse stuttering on high GPU/CPU load).
Huh? Weston has been using them since 2013 [1].