Nice appeal to authority. Are you referring to a formalised security model (of which I’d love to read more, if you have a link?), or the actual clipboard on your PC?
But not all interaction is equal. Access control and granularity of permissions is something X11 is sorely lacking in, which Wayland has built in. Which is why X11 is a bad fit for common treat models and Wayland is not.
Ohh, @LainTrain said so, so it must be true! I’ll let you keep believing that while I enjoy them and watch them grow in popularity and usage, just like Wayland.