[felizuno]

Check out The Immortality Key by Brian Muraresku, it has a few theories on through lines. The book is about these mystery cults, and specifically how they may have been using and early form of LSD. Part of the theory is the classically reported ego death experience might be what is referenced by the rebirth/resurrection claims. As for overlaps with Christianity, there are lots of fun theories including that John the Baptist was an initiate and may have actually initiated Jesus. This is a little difficult to square with the fact that the greek mystery cults claim to have exclusively initiated women, but hey they don't call them mystery cults because they are fully understood.

[panagathon]

That's only potentially true for the Dionysian. Others were open to both. See 76e in Plato's Meno, for reference.