WebDAV is what it is because it's designed (largely by Julian Reschke who also took over the HTTP spec from TBL back then I believe) to be addable conflict-free and routable without complex payload inspection to existing HTTP services/practices. Its use of XML can be regarded over-engineered, but it follows what was available and considered adequate at a time that had much much more consideration for interoperability and multi-party buy-in than is even conceivable today. I wouldn't dismiss it so quickly, especially considering WebDAV is an IETF RFC not W3C spec to begin with.