If you are speaking specifically about the tendencies of disparate societies to develop similar systems than the historian you ought to consider is Giambattista Vico and his book 'The New Science'. He specifically examines the problem which Herodotus (the greek 'father of history') and other grappled with since the early days of history. Herodotus noted that the gods of the Egyptians were essentially the same as the gods of the greeks but with different names. He supposed that the greek Gods came from Egypt and were simply repurposed. Vico disputes this point and argues that humans develop God's and Institutions naturally as cultures grow and that as cultures grow certain patterns naturally emerge.

A rather beautiful example which Vico supplies is as follows: "[men] created things according to their own ideas. But this creation was infinitely different from that of God. For God, in his purest intelligence, knows things, and by knowing them, creates them; but they, in their robust ignorance, did it by virtue of a wholly corporeal imagination...when at last the sky rolled with thunder and flashed with lightning, as could not but follow from the bursting upon the air for the first time of an impression so violent...and because in such a case the nature of the human mind leads it to attribute its own nature to the effect, and because in that state their nature was that of men all robust bodily strength, who expressed their very violent passions by shouting and grumbling, they pictured the sky to themselves as a great animated body which in that aspect they called Jove." (Vico, The New Science, 1725, 376-377)

Vico's vital point was two fold:

1. The ways that humans communicate is fundamentally related to the way that they perceive the universe.

2. As our tools of communication improve so too do the institutions we create (because we create our institutions in light of our perception of the universe).

To explain more clearly:

The earliest humans imagined gods to talk about their world and created institutions which accounted for the way they perceived reality.

As an example of this: (This account is from Herodotus, though I paraphrase) When Xerxes was invading Greece he had his men build a bridge over the hellisphont and the waves came and knocked it down. So he ordered his men to whip the waves into submission while they built the new bridge. Xerxes and his contemporaries perceived reality (water, trees, clouds etc.) as possessing some degree of agency and reacted toward reality as such.
Ancient oracles and omens and most religious practices are of this nature. They are appeals to a metaphysical power to 'act' in one way or another.

As societies grow more complex their language increases in complexity, and as language grows more precise dialogue concerning reality becomes more accurate. Consider that while the first men looking at a cloud saw 'Jove' we would see water vapor & whatever our weather app says regarding percentage chance of rain. It is not that the first men were 'dumb' but their language was imperfect and more akin to poetry than ours.

As language becomes more precise our institutions also become more precise and so instead of consulting the sacrificial chickens we use statistics to calculate and 'speak' in terms of accepted probabilities.

In short: coincidence doesn't work because if institutions are too similar their 'random' development is too improbable for coincidence to ever be a satisfying answer. Of course it is possible that it all happened by chance but again, improbable=unsatisfying. Vico's response is the most satisfying which I have encountered.

What I was really hoping was for an explanation why so many cultures have Dragon mythology. Which you prob said, I just didn't get.