I don't think that question has that much to do with prescriptivism and descriptivism. Prescriptivists want to use the study of grammar to uphold certain lingui

I don't think that question has that much to do with prescriptivism and descriptivism. Prescriptivists want to use the study of grammar to uphold certain linguistic norms; descriptivists find that language works fine without expert supervision; neither is a stance on the scientific origin of linguistic structure. You could be a prescriptivist and believe that grammar is a simplified model: you would just want that model to carry normative weight (e.g. for conservative reasons, or to promote standardized national language, or whatever reason).