No, scientism is simply the belief that the scientific method is applicable to all areas of intellectual inquiry, and that it's the most productive such method. The dismissal of philosophy is a straightforward corollary to that belief.

Note that the scientific method is self-correcting even in this regard: if someone can demonstrate a more productive method of inquiry, someone following the scientific method would accept that new method, just as they would accept any hypothesis that is demonstrably superior to the current state of the art.