The most overrated black musicians of yesteryear have been those who left the chitlin circuit, having been discovered by the hippies (or rather by the British musicians FOR the stupid hippies) and went on the mainstream white stage, and Las Vegas, people such as B.B. King, Ike and Tina (especially), Marvin Gaye, who went from a prime Motown hitmaker to a fighter for peace and social justice (yuck!), others, some to a lesser or greater degree. James Brown, Miles Davis. But you have know their early recordings to understand what was lost. Main stage is where everybody has to appeal to the lowest common denominator of the taste of the moment.
Sam Cooke was the best of them all, he blew Marvin Gaye away.