Fagen has a great ear and musical sense, but don't underestimate Nichols. Read about "Wendel" which he invented for Gaucho. https://en.wikipedia.org/wiki/Roger_Nichols_(recording_engineer)
How does Donald Fagen do it?
It seems, to my ears, that Donald Fagen is able to get an amazing sound out of a mixing board, much better than other producers can. I have read that he is a perfectionist and uses extreme attention to detail when in the studio. Do you notice the same thing in his recordings? A shout out to the late Walter Becker too.