A thought I had in the past was that Ancient Greek religion, or anything like that, would have a harder time standing up to a modern environment than the OTL current religions. There's less malleability in the face of science. It's more difficult, for example, when the rotation of the planets are discovered for the Hellenistic religions to make that work with the idea that Apollo pulls the sun with a chariot or that it's the Egyptian god Ra or whatever else.
So how would the Hellenistic Religions look in the modern world? How would they adapt to science and discovery?