Despite all of the discussion to the contrary, the gods WERE real
Much ink has already been spilled about Nolan’s grounded take, removing the gods from the story, and making interpretations of Zendaya’s character seem as if they are solely a manifestation of Odysseus’s guilt/regret. And, obviously that is the take the movie wants you to understand.
But, this does not exclude the fact that the gods were real, even if only Athena was shown.
What is the given purpose for Xenia? You should be hospitable to guests, and never harm them, in case they were a god in disguise.
The priestess beheaded at Athena’s temple WAS Athena in disguise. Her disgust at the desecration of her temple, and their willingness to kill a god under the guise of hospitality, is what sent the ships off course. Zeus and Poseidon were both real, as manifestations of thunder and storms, as was Athena.
Edited to clarify and expand on some thoughts