An X session depends on the main user process. Unless a DE picks the compositor as the main process then no, a compositor crash won’t affect the session. But they don’t do that, for obvious reasons, since the compositor is just a feature among others. They typically have a special program that takes that role, for example xfce4-session.
And one of the first points is how Wayland crash will bring down all running applications - yep, just like on X11! But it’s somehow Wayland’s fault.
They said that a Wayland window manager will bring down all apps, not a Wayland crash. Which, again, is not like it works on X, as I explained above. The window manager on X, like the compositor, is just another feature. If it crashes it just gets replaced and the session continues.