Wayland is very much ready for prime time. Many people have already been using it for years without any problems, and I myself have been using it without any problems ever since we switched from Plasma 5 to Plasma 6.
X11 on the other hand is no longer being maintained, it’s got plenty of vulnerabilities, and it works very inefficiently.
If you had read the first two posts on the Announcements > Stable Updates thread, then you would have known that already. 
Furthermore, People who continue running Plasma on X11 are on borrowed time, because KDE have already announced quite a while ago that X11 support will be completely dropped in Plasma 6.8.