Before I expand on my question, let me ask what I really should have asked before: is there a place I can look up what survives, with a rough classification; or better, what is believed to have existed?

You seem to include all non-fiction in philosophy. Fine by me, but I just want to make it explicit.

What I meant by proportion was the balance between fiction and non-fiction. I don't think I've heard of any Hellenistic fiction. Was it rarer than classical fiction? Was it less often preserved? Again because it was derivative?  But maybe we should distinguish science from philosophy. My understanding is that Hellenistic science was an awful lot better than classical science. Hipparchus was not lost because he was derivative of Aristotle, but, apparently, because Ptolemy was judged to supersede him, or at least be an adequate summary.