I don't think they're downplaying. Most users will be perfectly happy with the included KDE application for screenshots/screen capture (it is really fully featured, much better than the default options for Windows or macOS).
And they're not saying that no third party applications will work either, it is just that old screenshot applications that were created for X11 will need to be ported.
In the end that is not really much different from macOS dropping Rosetta in the next release of macOS (yes, I know there is a difference of effort). Old applications will stop working, applications that still get support will eventually support it (if they don't support Wayland already).
And they're not saying that no third party applications will work either, it is just that old screenshot applications that were created for X11 will need to be ported.
In the end that is not really much different from macOS dropping Rosetta in the next release of macOS (yes, I know there is a difference of effort). Old applications will stop working, applications that still get support will eventually support it (if they don't support Wayland already).