R&B and rock 'n roll BEGAN as virtually the same thing
R&B was supplanted by "rock and roll."
but it's revisionist to act like the 60s-70s-80s never happened.
No one here said that the "60s-70s-80s never happened." I don't really get what you're trying to accomplish here.
They splintered off into two distinctly different directions.
Explain when this supposedly occurred.
Doo-wop, funk and soul are closer to rock than metal and progressive rock. And all of those aforementioned genres have been called and treated as rock from their inception to now. The many primary and secondary sources will attest to this.
There is a wide musical chasm between The O'Jays and AC/DC
It's not wide because they're all still a part of the rock umbrella, just like punk and doo-wop are. A wide musical chasm would be between the O'Jays and Schubert.
For example, modern 'R&B' has very little to do musically with the blues.
Modern R&B has its roots in the R&B genres before it. What really makes it "contemporary" is its use of electronics and hip-hop and Michael Jackson-R&B-pop-styled influences.
Most R&B fans today associate the genre with uptempo pop songs and slick ballads--a far, far cry from what the genre was in its infancy.
Most R&B fans do not associate contemporary R&B with "uptempo pop" or "slick ballads." Those adjectives are reserved more for traditional pop or bubblegum pop or adult contemporary fare.
Music evolves. R&B evolved. It's still called "R&B" for a reason, that's the key word.
Especially considering rap music's history has already been convoluted in the way it has been taught.
You're not Bam and you're not Flash and the other early hip hop movers. They know what hip-hop really is more than you and I. If anything, they both decry just how ignorant a lot of people are of its roots and history, including these absurd narrow definitions of hip-hop.
You're view of hip-hop music is narrow.
Certainly the funk hip-hop anthem breaks such as "Apache," "Amen, Brother," and "In The Jungle Groove" are b-boy and DJ anthems and all vital to hip-hop culture and music.
Just because contemporary R&B is hip hop-influenced doesn't mean it's hip hop in the purest sense.
I didn't say all of contemporary R&B is hip-hop, and not all of it is influenced by hip-hop at all. I specifically just mentioned Mary J. Blige, and there are others in her boat.
For that matter, Justin Timberlake produces hip-hop-influenced pop music--it doesn't make him a hip hop artist.
Yes, each artist is a case-by-case basis. But he's not a "King of Hip-Hop Soul." Mary is equally respected by R&B fans just as much as rap fans for her unique hybrid style.
I don't think rap music has been canonized properly enough yet to start opening the floodgates for any and every artist in any genre that flirts with hip hop stylings or sound or aesthetic to be called 'hip hop.'
I'm not saying that every song that flirted with hip-hop is hip-hop. There are many electronic songs and a few full genres (breakbeat hardcore, trip hop, etc.), for example, that flirt with the genre, but are not treated as such.
Hip-hop music is more than just rap music.
Take a record like Shannon's "Let The Music Play" or Joyce Sims' "All And All." They're freestyle because of their sound (which was called "Latin hip-hop"), and features no rapping.
Hashim's b-boy electro-funk anthem "Al-Naafiysh" is virtually an instrumental, but it's still hip-hop. Planet Patrol's anthem "Play At Your Own Risk," a favorite with hip-hop DJs, breakers and early fans, is hip-hop, and it features no rapping and is essentially a variation of "Planet Rock."
Here's what Bam and Flash have to say about what hip-hop music really is: