Why Btonze Age?

[The Grand Nudger]

But what did the Greeks and Romans make of it? They laughed at the christian myths but still worshipped their own gods.

Not in the way you think.  Again, that's another christer fairytale.  

I think it's important to remember, the level of knowledge was much lower than it is today. There may have some select few really in doubt, not just about the foreigner's tales. Plyni the younger was the first to observe a pyroclastic wave in recorded history. Today we know, he described it correctly, but for the longest time, people doubted his account. Because they had nothing to compare it against. It's not even a hundred years that we have that level of knowledge.

Their level of knowledge regarding the existence of embellishment in storytelling was exactly as high as ours is today. In any case, in this example you present people doubting something, as I said, we've always been doubters. Every man who ever cried to heaven doubted the host when help didn't come.

It was much more common to doubt some tale back in the day, but at the same time still resort to the own tales. Since there was virtually nothing to compare it against. No reality checks of any kind. The ones leaving us written accounts were highly educated people by their standards. But the vast majority of people weren't. Not even in Roman or Greek time, when education was a little bit more common than it was in the middle ages or, if we take their contemporaries, in other regions of the world. But still, by todays knowledge only ten percent of Romans were literate.

Because your own tales are a cultural narrative regardless of whether or not you consider them to be literally true.  The greeks came up with euhemerism.  The romans worshipped the state. Uncle Ogg and Aunti Ugg knew that cousin BubBub was a bold faced liar.

The explanations for the various religions of the world are more complicated and nuanced than "people used to be dumb and believe dumb shit", know what I mean?