oral transmission of epics has been perfectly accurate
—
I believe that worked quite well for a very long time with the Iliad before Homer wrote it down. There are long traditions of stories that were transmitted verbatim back when people used to have aural memories which we have since lost.
“writing makes its debut in the subcontinent.”
That have been found - there are many underwater cities off the Indian coastline that are only partially explored, if at all, likely dating back before sea level rise during the end of the Ice Age or end or the Younger Dryas.
One reason for the claim of accurate transmission *is* the phony Greek Dark Age between the Trojan War and Homer, that doesn't make it evidence of anything. There are long (oral) traditions of (orally transmitted) stories that were (orally) transmitted verbatim (sic)...
A submerged town from the middle ages was exposed by the Boxing Day tsunami, and some statues where chucked up on the beach, but the sea still covers the town. That's on the east side of India. Off the west side, there's Dwarka, which *may* be ancestral to the Harappan civilization, which was apparently pre- and non-Vedic.