After a quick scan, Arcan seems to be pushing a microkernel approach, with some clients providing display server capabilities and others talking to them via shared memory. This will have the same problem as all other microkernels - nice for research, but the extra completely outweights the marginal benefits over a monolithic thing that generally has a smaller API surface to maintain.
Wayland design choices are heavily influenced by automotive and TV where it has been industry standard way before it became mostly usable as a desktop. And that has lead to design compromises that look odd on desktop.
But hey, you can probably run automotive UIs with your desktop compositor.
And Gnome devs are just being silly at this point.