A question like whether or not IPC and application buses are managed by a supposed display manager is a more complicated decision than it appears on the surface, with lots of questions that need to be asked that feel like you’re challenging the literal meaning of words depending on which contextual paradigm you’re approaching the discussion from.
The net result is Wayland being a reasonable solution to a real problem that still further isolates Linux into a GUI desktop silo. The result is only “cross compatibility” if you consider the “cross” to mean across Linux distributions, which - in fairness - is actually what most people DO seem to mean.