X11 is in practice network transparent.

That means that I can run a program, e.g. Firefox, either on my PC or on one of my servers, and I see the same Firefox windows on my display and I am able to use Firefox in the same way, regardless if I run it locally or on a server.

The same with any other program. I cannot do the same with Wayland, which can display only the output of programs that are running on my PC.

This an example of a feature that is irrelevant for those who have a single computer, but there are enough users with multiple computers, for which Wayland is not good enough.

Wayland was designed to satisfy only the needs of a subset of the Linux users. This would have been completely fine, except that now many Linux distributions evolve in a direction where they attempt to force Wayland on everybody, both on those for which Wayland is good enough and on those for which Wayland is not good enough.

I have already passed through a traumatic experience when a gang of incompetents have captured an essential open-source project and they have removed all the features that made that project useful and then they have forced their ideas of what the application should do upon the users. That happened when KDE 3.5 was replaced by KDE 4.

After a disastrous testing of KDE 4 (disastrous not due to bugs but due to intentional design choices incompatible with my needs), I reverted to KDE 3.5 for a couple of years, until the friction needed to keep it has become so great that I was forced to switch to XFCE. At least at that time there was an alternative.

Now, Wayland does not have an alternative, despite not being adequate for everybody. For now, X11 works fine, but since it seems unlikely that Wayland will ever be suitable for me, I am evaluating whether I should maintain a fork of X11 for myself or write a replacement containing only the functionality that I need. That would not be so complex as there are many features of X11 or Wayland that I do not use, so implementing only what I really need might be simple enough. The main application that I do not control would be an Internet browser, like Firefox or Chromium, but that I could run in a VM with Wayland, which would be preferable for security anyway.

In practice for some applications, for my purposes X11 forwarding never really worked (due to GLX and bandwidth among other issues). So that's 50/50 anecdote. I just checked and it appears Wayland adoption has helped push apps to adopt EGL which helps. There are tradeoffs both ways but let's not pretend X11 is adequate for everyone or every application. Subjectively, when I use Gnome now it's by far better than any version of desktop Linux I used a decade or two ago.