Hellenism definitely was a loose faith compared to Christianity etc in the 5th century.
No, it really wasn't a loose faith compared to Christianity. Not sure what you are counting as "etc" so I can't comment, but 5th century Christianity was *very* decentralized, heterogeneous, and localized. Hellenism wasn't any *more* centralized, but suggesting that it was less so is historical.
Now, if you were arguing that Zoroastrianism or Judaism were more organized than Hellenism (or Christianity) I would wholeheartedly agree with you.
If you want to know what Christianity (and Hellenism) were like at this time, I suggest reading;
*The World of Late Antiquity, by Peter Brown
*The Early Christian Centuries by Philip Rousseau
*Lost Christianities by Bart Ehrman
*The Cambridge Dictionary of Christianity
It's a common misconception that "the Chruch," (by which I mean the Nicine/Chalcedonian/Catholic/Orthodox church) was super centralized right from the start, or that it was unified in it's liturgy and doctrine, or that there was a strict church hierarchy. That generally didn't become true until the early middle ages, around the time of the Charlemagne bookmark in CK2, and was NOT true in the Migration Era.
Was Hellenism equally
decentralized? Yes. It was also equally centralized.