Michael Morris wrote
And if Brazil received more African Muslims than the American South (which one of your sources indicates), wouldn't one expect to find an even stronger Afro-Islamic influence in Brazilian music?

Micahel Morris, Brazil didn't have more African muslim slaves than America (upwards of 30% for the USA they say!) in proportion to their total amount of slaves. The reason the African Muslim element didn't show up in Brazilian music is because the dominant Bantu-Angolan-South West African drumming cultures drowned it out because they weren't supressed like in the United Sates.

Michael Morris wrote
Blues did not even coalesce as a musical form until around the turn of the century, at least, and plenty of 'white' musicians were playing bluesy material by the 1920s.

Michael Morris, Blues charactersitics and vocal form/techniques already existed before it was documented as a "form".