Eric Leiser (fairly knowledgeable fly tier) who wrote the book about the Dette's lists some bucktails and streamers tied by the Dette's in his book about them. I think they considered these to be flies - both Leiser and the Dette's:
A streamer or a buck tail is a sub-set of flies. Like a dry fly is, or a nymph is, but they are flies in their pure form.
A second page of the listing of Bucktails and Stremers tied by the Dettes: