Given the constraints of the column format, I think the "better approach" section makes a fair and accurate assessment of why REST isn't great. After all, the introspection file is just run-time WSDL.
Introspection says "post this kind of message here", where the message type is identified by the element name in the file, but defined out of band. "Post a resource" vs "post a schema-defined document" -- to me, the difference is theoretical; the cost described in the column. Time for me, I think, to give this debate a rest.
If you can't see the difference, or don't see it as important, then you're either not looking hard enough, or you don't understand the importance of constraints to software architecture.