>First paragraph

The argument posited was that Europeans during the "Dark Ages" were inferior economically and culturally to the Native Americans. There's virtually no point in history in which this was true.

>Could you share some source to support that, where people can read more?

The Iron Age

Prolific Written Language

Interstate Commerce

Sophisticated Art, particularly music

Prolific Agrarian societies

Prolific complex architecture

That's just a few examples. There's no single source, it's self evident when surveying the Early Middle Ages.