Hello soulcalm17

[Paleophyte]

Hard to reconcile Zeus with a Prime Mover given that he was widely recognized as the youngest of the offspring of Cronus and Rhea, themselves the children of Uranus and Gaia.

What we know with reasonable certainty is that virtually every Greek city, town, and hamlet had their own patron god, or goddess and sometimes more than one. We don't see them giving those up in favour of Zeus, which is what we'd really expect from any move toward monotheism.

Hard for modern people to do this, I suppose. Not so hard for them. Greek and Roman myths were malleable and frequently contradictory. For example, Eros is Aphrodite's son but also existed before she did. 

You remember Plato's Symposium. They change the myths all around to illustrate the philosophical points they want to make. 

Later Roman thinkers influenced by Neoplatonism could take a name and plug it in where useful, and not worry about strict adherence to writers like Hesiod.

And that religious plasticity is probably the best argument that could be made for polytheism. Monotheism begets orthodoxy and rigid intolerance. The wonderously varied and hellishly contradictory Greek mythos could never have existed under a monotheistic mindset. Instead you see tolerance and acceptance of foreign gods leading to a rich syncretic mess in Rome, because it's just plain dumb to annoy anybody's deity. Importantly, you don't see the opposite. There's never an evangelical drive to export the Olympian deities to foreign shores. Rome borrows them and rebrands them but that happens because the early Roman Republic lacked any major deities of their own, being more involved with local, domestic, and familial spirits.