You're being absurd. I already covered all of this in the OP and gave you very concrete examples of how we know things about pre-literate cultures.

And what are you even talking about? Of course there is a Kurgan culture.

"Scholars who follow Gimbutas identify a "Kurgan culture" as reflecting an early Proto-Indo-European ethnicity that existed in the steppes and in southeastern Europe from the 5th millennium to the 3rd millennium BC. In Kurgan cultures, most burials were in kurgans, either clan or individual." Kurgan

Kurgan culture | prehistoric culture

I don't have any more time to devote to this.