On the contrary, it is useful to have a comprehensive, substantive measure of technical skills. Having one does not preclude additional assessments, as you assume. I have been continually disappointed with the lack of extensiveness in technical interviews, as a candidate, but also as an interviewer when reviewing other interviewer assessments of potential candidates. I have yet to meet a programmer who doesn't believe they are very good at what they do and I believe this problem is due in large part to the shoot-from-the-hip approach that the industry takes at the interview stage.