I agree that Eric Clapton is a part of the blues. He's a blues "revivalist" although not part of the tradition. PPM and the KT are a part of what the music business chooses to call "folk" these days but they are not part of any specific folk tradition that I know of. The three subjects above are professional entertainers and do well at it. I admire their work, particularly Mr. Clapton. But they are not their traditional sources. Their relative importance is based on what one considers important. As to "illuminators", well I'm not so sure. Maybe Mr. Clapton because he really has studied the traditional blues style as has Bonnie Raitt and others who are pop stars. Bonnie has done a service by touring with "Sippie" Wallace as an "illuminator".
Robert Johnson, Bill Bill Broonzy and Mississippi John Hurt reflect a body of traditional African-American music as having been born into that culture that created that music. Eric Clapton is an entertaining musician who has managed to imitate sucessfully a blues style and there's nothing wrong with this. But he is not inherently part of that tradition because he is from a different time and a different culture. This is evident in the kind of music the traditional musicians have selected which speaks to their cultural environment. Mr. Clapton is a sucessful pop star and speaks to that business climate. I have no problem with his personal success and am happy for it. Same for PPM and the KT. But a disservice is done to the African-American tradition of the blues if the general public feels that it's represented as a tradition by Mr. Clapton.
Frank Hamilton