Try reading Elegant Hipsters, Fagen’s autobiography.
He is painfully honest about his character and his world view, and his defence, which was to adopt a cynical and ironic distancing style. I feel the songs capture and express this very well.
To my mind, he found a match in Walter Becker, and between them they confected the Dan sound from their deep affection for American music, which arises from colossally dysfunctional American culture. For me there is a very powerful effect created by this queasy juxtaposition of The Great American Songbook and existential dread.
He articulates all of this better than I can in his book, which is well worth a read.