For me it seems more realistic to frame the discussion as a continuum with content and development as the opposite poles. There are technical writers at many points along this continuum depending on their requirements, their preparation for future work, and even their personal interests.
Technical writing is an interdisciplinary field already.
XML is just the latest edition to Human Factors, Rhetoric, Business Management, Composition Theory, Cognitive Psychology, Instructional Technology, Linguistics, Sociology, Knowledge Management, Object-oriented concepts, and Systems Theory. XML is another tool. For example, compare the work of writers using FrameMaker expertly with others who barely know how to use it. For one, the tool is a means to an end. For the other, the tool is an obstacle until they get past the learning curve.