Of tales which have survived through millennia, we can be sure as to their gravity. We strongly relate to them. Why else would they survive, reemerge or have the power to change one's convictions? Ever since speech first took place, the ideas within the stories and dreams we have conjured up have had to stand the test of time. Only the common themes among them; the most repeatable; relatable; and true (true from the human perspective) makes it to the end, written or not. These are so refined that their significance becomes religious.
To me, it matters little if the ideas we have come to call gods are found outside or inside the mind (is this distinction even possible?). They are equally true regardless.