funk and disco are R&B...before the term disco came along, Soul, Funk, and Jazz (uptempo) were the actual tracks being played at the Disco's
60s/70s were more to the ORIGINAL soul sound
..not really
90s was better than the 80's
Funk and Disco were offshoots of R&B. R&B is actually much closer to Blues, while Disco and Funk were heading more in the direction of Rock and Roll. I am no musicologist so I don't know where the dividing lines are, but there are and were dividing lines. Look at the career of Johnny Taylor. He went from Gospel, to Blues to R&B to Disco. There were clear dividing lines in the music. Joe Simon is another guy that went through all of those genres and then he went into Country music. Otis Clay is another guy that went through genres.
Btw, some of the 80's music was excellent. Stevie Wonder, Michael Jackson, Luther Vandross, Phyllis Hyman, Freddie Jackson, Kool and The Gang, Prince, Ashford and Simpson, and Stephanie Mills etc., put out excellent R&B songs during that era. Stephanie Mills was great in the 1980's.