@satam55 I make the point that the decline of r&b actually begins in the late 80s to early 90s, as rap emerged as the preferred, better-selling form of popular black music
The 1960s and the 1970s are the prime decades for soul/r&b: Motown, Stax, Philadelphia International, SOLAR, Soul Train.
Nelson George wrote the book, "The Death of Rhythm and Blues" in 1988.
By the 1990s/2000s, most of the successful r&b that remained was basically a fusion of r&b and rap: TLC, Brandy, R Kelly, Usher, BBD, Destiny's Child, etc.
The classic soulful sounds that we heard from the Four Tops, Fats Domino, The Supremes, Aretha, James Brown, Maze, Bill Withers, Anita Baker Barry White, Roberta Flack and Luther were largely gone by 1990.