if you have a chance to take a deep dive into david's work you'll see that the myths go way way beyond navigation stuff. we're really talking about a system of perennial wisdom. bible stories in the sky. homer's iliad in the sky.
1. We have to have them, as they enhance significance.
2. There are only two places to 'have come from' in a cultural oral history - The Sky and From Under the Ground.
3. Mythologies are subject to Asch Conformity and are accretive.
But that being said - my skepticism stops there, because I do not know enough about this topic yet. Will go more in depth.