I think of Roger Miller as I like his version better but that's a good point. Kris Kristofferson is a great example of a very good writer who was a decent to mediocre singer and performer. No one considers him to be a great artist even though he was probably a great writer.Case in point, "Me and Bobby McGee". Who does everyone think of first when that song is mentioned? Janis Joplin, the singer, or Kris Kristofferson, the writer? "All Along the Watchtower" is another one. Most think of Hendrix's version and not Dylan's (the original).
"Hurt" is another example. Johnny Cash didn't write it but he sung/performed the definitive version of it. Neither Johnny or the song are in anyway lessened by him not writing it.