Great post, DL.
Prolepsis is an empirically derived, bottom-up process in which general concepts are formed through accumulated exposure to particular instances.
By my reading, this is where DeWitt's focus on what Velleius has to say in "On The Nature of the Gods," rather than solely on what Diogenes Laertius has to say, places Epicurus closer to what you are describing as the Chomsky position. I've never read anything about Chomsky and I have no ability to comment there, but maybe this is more similat than just in result.
Prolepsis is an empirically derived, bottom-up process in which general concepts are formed through accumulated exposure to particular instances.
As I read it this last, statement here is definitely the prevailing view of Epicurus (based mostly on the relevant part of Diogenes Laertius) but DeWitt argues that Cicero's summary of Epicurus' view is not limited to this and reads more like you are describing as "The grammatical structures underlying all human languages are not abstracted from repeated sensory experience but are instead manifestations of an internal, species-specific cognitive architecture."
If someone were looking to explore parallels between Epicurus and Chomsky I'd definitely recommend DeWitt's chapters on anticipations and the gods.