What elvis did is bring rock & roll into the American mainstream. This was a time when people like Little Richard Chuck Berry and Fats Domino were not getting airplay on mainstream (ie: white) radio.
Elvis opened the door and they followed while leading. The Stones, Led Zeppilin and others from that era knew and will tell you where their music came from.
It was/is white America that had no clue.
Well, we all know that stopped---dead---cold. Vocal music by black artists was popular simultaneously; The Platters, The Bluenotes, lots of them were around at the time. For some reason, that music survived and morphed (not a big stretch at all) into the sounds of Motown, Philly and a few places in the Deep South. By the end of 1963, African-Americans had pretty much abandoned Rock and Roll.
They moved on while the rest of North America shifted to commecial rock. Hmm... brings whole new meaning to 'Out Of Africa'.