T&B, funk music is not rock n roll. it is it's own monster. I try to define rock n roll as riff-based. a band without guitars like Morphine is rock n roll (or "low-rock" as Mr. Sandman would describe it, RIP) because the tunes are based on riffs.
other genre's, funk, ska, reggae, eetc, while sharing instrumentation with rock and cohabitating with rock, are not about the riff.
James Brown was never rock. he was a soul singer who helped create the genre of FUNK.