First World/First Reflection?

[Naria]

In addition to Moose's post, keep in mind that they Ascians have been interfering in our civilization and the other worlds' for longer than we have records for. On the Source that interference has taken the form of periodically burning civilization to the ground, but we don't know what from that interference would have taken on other worlds besides having the ultimate goal of aiding Zodiark through the Rejoining. If the other worlds don't have Calamities, they could very easily be more advanced then we are. Or with out the Ascians constantly causing world wars and pushing tech forward they may be less advanced then we are. It depends on what the Ascians view necessary; they could have encouraged similarities or differences between the Source and the other worlds or just let things go as they would so long as it didn't threaten the balance. It could be all of the above, depending on the whims of that world's Ascian Overlord. So really how alike or different they are is up in the air at the moment although it has been stated that they are not "parallel" copies.

Spoilers for the Warring Triad:

For example the events of Unukhalhai's world that lead to it becoming Void certainly don't seem to have had any parallel in Eorzean history (although admittedly that would have happened in a time that records are scarce to non-existent)

Really using the Ascians as I mentioned would be a way for SE to justify similarities or wild differences in the event that we ever have more interaction with the other worlds.