Two more points.

As I understand Scott's argument, it's not that the blues *did not* or *could not have* originated in "the Delta," only that the evidence for the claim is not very strong, even if it has been repeated so often as to be taken as fact.

Also, it seems likely that in the days before radio and blues recordings," an innovation in musical style like the blues must have taken some time to circulate over a wide area.

Here's a contrary suggestion: Did the success of "Memphis Blues" trigger a blues-making craze?

It certainly mainstreamed the style in an unprecedented way.