I like Dylan, but think you may be overstating the case of his being the first to write his own music. Of course there were the politically minded folk singers that influenced him, many country stars, and the blues singers writing their own material. But you also have more popular artists like Buddy Holly, Bo Diddley, Little Richard, Jerry Lee Lewis and others.

I will credit him with expanding the general public's notion of what could be sung in popular music, but saying he was the first to sing his own material either in terms of a political or popular artist isn't really accurate from my perspective.

Positively 4th Street is still a kick ass song though.