I guess Sinatra doesn't make the grade, either.
I would bet that Cash wrote more of his songs than Presley did.
Johnny Cash lived thirty more years than Elvis did. Not only that, most of Presley's compositions were hits. Whereas many of Johnny Cash's hits were written by others. Yes, Johnny may have written more songs, but it doesn't make him a better artist than Presley, IMO. As for Sinatra, he was a good singer, had great charisma, and was talented. All similar attributes to Johnny Cash, and thus, again IMO, nothing that makes Sinatra or Cash great artists. You could, using my logic, say the same of Elvis Presley and I wouldn't argue that point much. My opinion of popular music "artists" is that those terms are somewhat contradictory. Popular cultural entertainment, IMO, is not art. It uses aspects of art, such as music and acting, writing or graphic arts, but it does not strike me as art.