If this theory was correct we'd expect the various forms of evidence of belief in these different supernatural creatures to suddenly appear in the record. To take an example I'm familiar with, in Paul Barber's Vampires, Burial and Death (Yale University Press, 1988) he points out that in archeological record you find evidence that is consistent with later recorded practices against vampires: bodies buried face down, bodies buried decapitated with the head down, bodies buried with a nail driven through the tongue, etc. But these sorts of practices among limited individuals seems more like a longstanding thing rather than appearing in a distinct horizon.

Instead he postulates that both the werewolves and vampires of folklore (as opposed to fiction - no pale, attractive fellows you could mistake for the living here) arose as explanations of the natural consequences of improperly disposed of bodies - bodies that were buried too shallow and dug up by wolves or dogs, bodies that were buried in soggy ground and floated to the surface as if risen from the grave, bodies that were buried in rocky soil and failed to decompose as quickly as expected.

If you're really curious and not at all squeamish about frank descriptions of rotting bodies, it's an interesting read.