I Started reading the greek plays and other authors and get into this doubt. How much of the greek mythology was really a religion and how much were entertainment/known to be fiction? At what point the history of the gods and heroes were only dramaticized and written down the real religion or were just free-style entertainment?
Lets say that if future historians could look into the vast comics/movies/screenplay, how to differentiate Marvel universe from the many "real" religions?
More can be said—and I know a thing or two about Greek theatre, if you want more from that perspective or have more specific questions about the relationship between mythology and plays—but for now I’ll point you to these older answers:
Did ancient Greeks literally believe in their myths? by /u/UndercoverClassicist
How do historians/anthropologists distinguish fiction from religious stories? by /u/sagathain