Those myths and legends are old enough to contain traces of shared Indo-European beliefs, so the real old stuff should be found, in some form, in other cultures, like Greek or Norse mythology. But I don't think it is true in this case

> shared Indo-European beliefs, so the real old stuff should be found, in some form, in other cultures

No, this is pure speculation.

While there does seem to be some commonalities (ancestral) it is also the case that entire species lived in different parts of the world following different timelines and experiences with no knowledge of each other's cultures. Thus not everything can be mapped to common ancestral factors.

That is why Sanskrit literature is so fascinating since there seem to be records of "different types of people" coexisting. Note that i am merely drawing parallels and not that they were actually distinct species of Homo.