Has anyone read the Gene Clark bio "Mr. Tambourine Man?" It is such a sad story - intense stage fright, distaste for touring and traveling, endless substance abuse. In some ways, he never really got his career into a consistent groove after the Byrds. On the other hand, he made at least 5 really solid albums after the Byrds, created a substantial body of work, and wrote at least 3 tunes that have left a lasting impression, at least on couple of generations of listeners.
I have been listening a lot to the 2-disc "Preflyte Sessions" from 1964, most of which consists of Gene Clark songs - many never recorded for Columbia. While McGuinn's 12-string Rick and Crosby's harmonies in many ways define the Byrds sound, I still contend that Clark's songs were the best material they ever did. That said, "Younger Than Yesterday," recorded after Clark left, is a pop/rock masterpiece. IMHO.