Why do you think 5 years is an unreasonable amount of time to see major traction for such a project? For that matter, why would 8 years be unreasonable? X is 30+ years old, Wayland is less than 1/3rd the age. The amount of available people for work is not static or even well defined. The systems Wayland integrates with (DEs/login managers/WMs) and replaces are deeply integrated across our ecosystem. And this new design is completely new, so it will take time and a lot of upstream coordination to make progress. They also have gone out of the way to do things like provide continued X support through XWayland on top of that to lower the barrier to moving forward on it. This will help accelerate Wayland's adoption, and allow applications to move to it quicker (and distros can ship Wayland, rather than maintain X11 and Wayland).
Do you think 5 years is bad because the developers just didn't like, invest enough free labor in the project to satisfy your arbitrary requirements, or something? Did they not work hard enough? Was the job actually easier than they made it seem? Would replacing it in 3 years have been acceptable in your "book" of requirements? Inquiring minds want to know what your book says.
I ask this seriously, even if it may come off as slightly annoyed. I think that's reasonable levels of annoyance. Your reply comes off as extremely ungrateful, IMO. I ask that you seriously, sincerely think about why you believe this is "bad progress". Do you have serious reason to suggest they have messed up somewhere, that they have failed to deliver on promises, or do you just "think" that it shouldn't have taken that long and thus, it is bad? Or do you believe X never needed replacing (and why do you think that, vs the Wayland developers, most of whom are prior X developers)? "Thinking something" you can't verify isn't the same thing as actual knowledge.
People who work on open source and free projects invest real time, labor, and life into them, much of it thankless work, on projects like Wayland -- even if the projects themselves are good and that "thankless" work vital. Even if they take years to realize. Why? There are a lot of reasons, really. But none of them involve wanting to have people judge them with no context, by arbitrary standards of how good they are as software developers, or something, because they think it "took too long". That's the kind of shit people make fun of managers for saying!
Please note I'm not affiliated with the Wayland project in any way, but I have my share of experience with doing maintenance on large open source projects. When people say things like this, it comes off as ungrateful, as if I haven't given enough free labor to satisfy you or your desires. Maybe I should have worked 80 hours a week instead to deliver it to you "on time". That might have satisfied the requirements in your "book", I suppose? Or maybe I should have just not written the software at all, and left you on your own, whatever the cost of doing that is.