> you will actually find them to be smaller than the respective X11/XCB backends there, for various reasons.

It doesn't seem surprising to me. As X.org has gained extensions over the last 30 years, toolkits that speak X11 find themselves having to decide which extensions they'd like to use. Adding flexibility on this naturally leads to a bigger feature matrix. Of course, the toolkits are also free to drop support for X servers that don't have those extensions, which in turn would shrink the X11 backend.

I have no doubt that in 30 years, they'll have a similarly-sized feature matrix for all the Wayland extensions they'll want to support.