Perhaps I am missing something but it seems to me that a world in which Godzilla was common knowledge would have a completely different history of biology. For one thing it's hard to imagine that explaing Godzillia would not be a major goal of philosophers and scientists since the earliest days.

I imagine one of the basic questions would be whether Godzillia was a beast or a god and answering this would be a high priority. What does Godzillia want? Where did he come from? Has he always existed? Are there more? Do they mate?

These seem like really big deal questions when confronted by a sea monster which occasionally destroys towns.