"... early Delta blues... has a primitive sound..."

People have associated the (artificial) notion of Delta blues with Charlie Patton's growly voice because he happens to be the most notable blues singer from the Yazoo-Mississippi Delta born before 1895. But we don't have reason to believe his style was particularly representative of his Delta peers of 1910-1919, which was 10 to 20 years before he began recording. E.g., James McCoy was about the same age as Patton, Son House learned "My Black Mama" from McCoy, and House said McCoy sang similarly to Skip James.

We also don't have any better reason to say Patton sounded primitive than to say e.g. Henry Thomas (Texas) and Peg Leg Howell (Georgia) sounded primitive.

We can identify a significant link between work songs and blues songs, across the South, but Patton's repertoire isn't somehow special to identifying that and the Delta isn't somehow special to identifying that.