Apart from the huge range of styles that Elvis was already covering during the 50's, a much bigger one compared to the other rock pioners, Presley music evolved far more during this same period. The '56 N.Y. sound was far removed from the Sun era, the '57 Radio Recorders material was another step further, the Nashville '58 sound was something else compared to his earlier material, and the March '60 Elvis is Back sessions showed and artist that was maturing eons beyond the cats that started back in '55.
With the exception of Ray Charles (not exactly part of the original rock and rollers) by 1960, Jerry Lee Lewis, Chuck Berry, Gene Vincent, Bo Diddley, Little Richard, Perkins, did had on certain degree, the same sound they had in 1956, not Elvis.
Elvis is Dead? By 1967 most of the original rockers were doing pale covers of their old hits, or resting with no money over an old couch. Presley was winning a Grammy, and despite criticism of his movie soundtracks, at least, until '65 those were still Top 10 albums, others 50's rock and roll acts were dead by '63, Elvis was still making millions a year in '67.
1969 some of those original rockers got relieve with the 50's revival, Jerry Lee found a career in country music, but nobody of this generation ever delivered a modern current sound again (at least not with chart impact), Elvis did it, he was not an oldies act, in '72 but an act still going. Berry's My Ding A Ling? just a novelty record.