This would be a reasonable thing to believe if plato didn't frequently make up tales like this as allegory out of whole cloth, including more than one example _

This would be a reasonable thing to believe if plato didn't frequently make up tales like this as allegory out of whole cloth, including more than one example _in the same dialogue_ There are multiple examples of 'myth-like' stories whose only attestation is a platonic dialogue. https://en.wikipedia.org/wiki/Myth_of_Er https://en.wikipedia.org/wiki/Myth_of_Er here's another example.