I don’t think this is true at all, cause R&B was still legit well into the 2000s. Rappers wanting to “sing” and singers wanting to rap is what killed R&B. Instead of putting R&B singers on hooks and bridges, rappers basically started signing themselves, and ditched bridges. I’d say to directly pintpoint it, you’d starry with T-Pain in 2005. Every rapper started to hi-jack him. Then here comes Jay-Z with “Death Of Autotune”, thinking he’s about to do away with it, and it literally explodes after that, having the opposite effect of what was intended.
It was a slow and progressive death. You look at the each decade got progressively worse. When they put the label “queen of hip hop and R&B” label on Mary J Blige, at the time it seemed insignificant but by the time you got to the early 2000’s the vocal quality had diminished and the production was mostly hip hop.
Record labels stopped developing R&B artists altogether. Some of them would sign to rap labels and they wouldn’t get any assistance.
Rap infused itself into the genre, and it lost its identity. R&B singers basically started singing rap lyrics.
And the crazy part is white artists would use black music to boost their brand but go right back to their own.
U can even say rap music in general has contributed to the erosion of the black community.
It popularized gang culture starting with NWA and Ice T.
It popularized selling drugs and using drugs
It glorified and objectified black women
With each era, it got progressively worse.