Small add-on to the OPs question. How much (if any) of Hellenism got persevered in the Catholic and Orthodox Churches?

Sort of a big question, and I’m not necessarily an expert, but bear with me. Hellenism didn’t necessarily decline, primarily because Hellenism wasn’t something that was explicitly “followed” in a religious sense. Hellenism is more of a description of Greek culture. The Greeks referred to themselves as “Hellenes,” and their culture became known to us today as Hellenism. It just refers to Greek traditions and ideas, like their philosophical, educational, and political ideals. Traditional Greek Hellenism influenced many different cultures both west and east of Greece and hellenized them, by passing on some of these ideals and influencing the development of their societies.

The Romans went through a period of hellenization, but we still refer to them as Romans and know that they followed their own pantheon of hellenistic deities, which were influenced by the Greek culture. Virgil’s “Aeneid” is a “Roman Epic” that shares a lot of similarities with Greek epic poetry, and shares themes with Greek mythology. Emperor Marcus Aurelius wrote about his Stoic philosophy in Greek prose. Hellenism influenced cultures in this way.

So the influence of hellenism didn’t necessarily decline, but rather kept being adapted by different cultures as time went on. If you really want to look into it and speculate wildly you could argue that most modern societies were influenced by hellenistic ideals that were passed on from society to society after two thousand years. There were periods of hellenistic revival (like during the renaissance) where Greek philosophers were “rediscovered” and had massive influence on social or spiritual movements, which we know had a massive influence on the state of todays societies.

We probably don’t think much of being Hellenistic today because we’re so far removed from that culture.

Edit: I’m interested in hearing feedback on my response, I’m just a lowly senior undergrad student who’s done a fair bit of work on topics like this.