Wayland has mostly positive user reviews because it presents nicely to the user (VRR, scaling, etc.) On the developer front it seems there's a lot of struggle over things that were solved in X11 but for some reason require a lot of debate in Wayland.
- There's still no way to universally configure monitors and input devices, so the startup cost to checking out a new "WM" (compositor in Wayland terms) is non-zero - you have to reconfigure everything from the ground up, and for anyone with complex input systems (see: accessibility devices) this will take a lot of time because each compositor insists on using a different format for configuring these things.
- Each compositor is tasked with coming up with solutions for all parts of the user experience (hence the last point) and thus anyone who wants to experiment with making their own WM now has to worry about a billion things that wouldn't have had to deal with in X11. Yeah, there's libraries for dealing with that stuff, but it's not as simple as it was and lot of innovative WMs won't ever be able to make the jump.
These are the two biggest issues I can see that are entirely chalked up to its design. Technical issues (like the "load balancer" thing that keeps Firefox from crashing on Wayland) will be solved in time. However, the above points are unlikely to ever be addressed. Should they be? I don't know.
Switched from BORE to EEVDF (which is now the stock scheduler after 6.6 IIRC.) EEVDF works better under load.