I would disagree. Here is a record of music from Mali recorded in the 1950s (I have the vinyl in my old-fashioned ethnomusicology collection), and if you go to about 6:05, there is a recording of a woman singing the praises of various Muslims. I have played it in music classes, and asked students who she sounded like; the usual opinion is Aretha Franklin, but there are blues and gospel singers from the early 20th century who would also fit.
Also, the "blues third" is a note that isn't part of the European 12-note chromatic scale; it's a frequency ratio of 11/9, halfway between the 5/4 (diatonic) major and 6/5 minor thirds. The earliest singers brought from Africa probably tried to emulate it on instruments they co-opted, such as the banjo and guitar, and later the clarinet--and of course their voice. The result is music that is European in form, but African in tone.
And if you go back far enough, there are hints of "blues" in English and Scottish folk music.
Have you ever heard "IN THE PINES" or "THE HOUSE OF THE RISING SUN", in the original versions? Heck, even more modern versions, from the 1950s will do. :-)