It's a good sentence. I can't easily fault it. Especially if you're going for a slightly poetic tone. Writing is whatever you want it to be. For me, it's usually about clear & meaningful communication, but there is plenty of variation in this depending on the message, the audience, the medium, etc. Consider what is the primary goal of your sentence and what is the best way to achieve it. Depending on the goal, you may or may not wish to cut out a lot of words and get more quickly to an example.

It's not wrong but it's not the easiest sentence to read either. It could be more elegant and precise, as you say. I feel like I want to put a comma after "once," also, just to make it a little more clear. I'm not sure if it's strictly correct but to me it makes it easier to read.

I think the sentence it fine. Whether you tend towards precision or elegance may depend on whether you are a scientist or a poet. In my opinion, good writing is both precise and elegant.

It is a good sentence, but use the present tense: "Traditionally, a myth expresses..." Past Tense feels inappropriate because "a myth expresses..." is a timeless thought. Use Present Tense for timeless thoughts. The balance between precision and elegance is a matter of style. It is the prerogative of an author to decide.