Historically it is false to say there was only one religion. You cannot prove there was one religion ever. All evidence is to the opposite. Worship and veneration appears to have arisen from hunting and fertility rites where many gods, spirits, plants (especially psycho-active ones), animals phalluses and yonis were worshipped all over the planet.
I think you are forgetting about "Islam" and by Islam the way of worship that began in the middle of The Cycle after the fall. In fact, I haven't heard much said at all about what kind of religion this actually was? We know there was idol worship and we know fertility played a big part.
The types of things you listed I have a strong feeling all came into existence around that time. Golden and Silver ages being totally natural are not going to leave anything for us to find ... but after the fall into duality these gross things of Bhakti are going to begin to be wide spread. I have a feeling that Islamics, or at least the part of that branch, have placed some kind of role in the existence of old traditions even in the newer lands. Before the actual religious fathers managed to establish their religious kingdoms there. They needed something to be converted from right?
All this whilst the true Bharatwasis were still doing pure Bhakti. The Islamics were really shaking things up, dabbling in magic and science and expanding their influence after being booted out of Bharat for using the corrupted organs and influencing mother earth. In regards to all these pantheons of gods etc in my own personal opinion there IS one specific set of soul/s which these stories were based on.
Each religion/people has known this group in their own way however essentially they are the same souls. We know there is 12 souls x 9 religions in the 108. For me it would make sense that maybe if each culture/religion is not worshipping the exact same gods ... they are worshipping their own section of the 108 within which particular souls from each 12 would possess a similar individual quality with the same number in the other sets of 12.
Comparison between Jupiter (Roman), Zeus (Greek) & Thor (Norse) & Indra (Hindu/Jain) & Sakra (Buddhist) ... will bring up many of similarities. I am not saying i've really researched it in depth but its definitely interesting.
I would also point out that what i've typed out is just speculation something that came to mind.