Dean Porter, a Nashville Guitarist for many years, told me this story. Cash has just finished the Folsum Prison Blues session. As they left the session someone asked Luther how it had gone. Luther said terrible. They asked him what went wrong. Luther said I played way over my head... I'll never be able to do it on the road.
Most guys with a Fender Tele, a Twin Reverb amp and about 5 lessons can do a good job on Folsom Prison.
But there was not one guy in 10,000 that could create guitar licks with the appeal of the simple lines of music Luther could do at the drop of a hat. Lots of Guys could play Folsum..after they heard Luther do it. They could do it in their sleep. But few if any could have created the simple licks Luther played on Folsum.
I think Chet Adkins said it best. There are a thousand guitar players that can play complex licks that impresses other guitar players. There are a lot of singers that can really impress other singers with their vocal skills. But only a very, very, few can play and sing new music that the fans want to listen to.
John and the Tennesee Two-Three could do that better than a lot of far more accomplised musicians.
Cash used to object when other performers would refer to him as a singer. He would say.. I may have a style that some folks like.. but I am nothing near a singer.
I think the term for Johnny Cash is he was what he was. He was genuine. He never tried to be anything but himself.
Amen, that's why Jimi will always be the greatest rock guitarist ever, he did it first.