I do not know who your audience is. In any case, it sounds like you might possibly have 3 working papers in mind, if you did ever follow that scheme. (1) Noir films, you suggest, are the product of two separate and distinct things: social influences and narrative influences. And then you allude to a third influence "changing approaches to filmmaking" that did it in. (2) Noir origins. (3) How the items in (1) manifest in the two main noir centers (America and France).
By the way, I can understand Hollywood's predominance, since it had that in other genres. But why France? That should make an interesting story.
Who are these "folks" that do not accept French noir as on the American level? Have they had the exposure you've had?
I do agree that before you can tackle (3) above, you need to finish your French noir book first. Maybe you already have. And the latter project is indeed a book-type thing, not a working paper thing.