Also, I did not claim that it was "borrowed" in a simplistic fashion. Source criticism of the Pentateuch has moved beyond the mere isolation of strata. What does seem likely is that the human authors of Genesis 6-9, under divine inspiration mind you, and aware of the traditions about a Great Flood that preceded them and that existed in other cultures, traditions that suggest a certain viewpoint regarding the relationship between humans and God, crafted their own Great Flood story, drawing on similar motifs but radically altering the message.
As for scholarship, a quick review of the books on my shelf demonstrate amazing unanimity on this point: see Blenkisopp (Pentateuch); see Whybray's article, "Genesis," in the Oxford Bible Commentary; see C. Westermann's Genesis 1-11; see the relevant sections of K. Sparks, The Pentateuch: An Annotated Bibliography.
That seems unlikely. There is no evidence to support your claim, only speculaton. Do you think that maybe-- just maybe Genesis predates the other flood stories? Who sent the flood? The gods of Gilgamesh? It seems that those who find a relationship between Genesis and other ancient texts reject the idea of a worldwide flood. IOW presuppositions trump manuscript data. For a technical but fascinating examination of the evidence, see I Studied Inscriptions From Before The Flood, Ancient Near Eastern, Literary, and Linguistic Approaches to Genesis 1-11, Volume 4, 480pp. There are 25 scholars who contribute to this volume. Your position does not hold up.