The biggest thing I can think of is that X11 is more flexible when it comes to specifying custom resolutions; which some people use to output 240p on CRT TVs for emulation. AFAIK, there is currently no real equivalent for xrandr on any Wayland compositor.
I’ve also noticed that Grsync’s password prompt is broken on Wayland. Thankfully, it has a feature that lets you preview the command it’s about to run, so that you can copy and paste it into a terminal.
Being a KDE user on EndeavourOS, I use Wayland everyday. I switched over a few years ago for Waydroid, but now X11 isn’t even an option for me with the current release of KDE.
wayland dwms can and do absolutely implement that. For example kwin has a setting to let programs access keyboard input in the X11 way for the old method of global shortcuts. And to disable the framebuffer for fullscreen games.
If you wanted, you could probably write a wayland compositor that has all the X11 apis that old management tools use. Wayland is just an api at the end of the day.