Sorry, I know this nonsense from Daniel Stone I am interested why you believe it.
"compatibilities which are irrelevant" do exist, such as old drawing primitives but those are not really an issue. They can be maintained for backwards compatibility and eventually deprecated and removed, but they are not anything which holds back modern clients. The X server protocol is not anymore a "pointless middle man in that exchange" than the Wayland protocol is a "pointless middle man". A protocol is obviously needed so can not be pointless.
I believe it for the reasons explained by Daniel Stone, there is no difference between my opinion and his on the topic of X's inefficiency as an IPC middleman.
"compatibilities which are irrelevant" do exist, such as old drawing primitives but those are not really an issue. They can be maintained for backwards compatibility and eventually deprecated and removed, but they are not anything which holds back modern clients. The X server protocol is not anymore a "pointless middle man in that exchange" than the Wayland protocol is a "pointless middle man". A protocol is obviously needed so can not be pointless.