Well, I'd disagree with that, as my favorite director has imo made only two flawless masterpieces. But to be honest, I haven't encountered a director yet who has made more.  
Good idea with Down by Law. At first I didn't feel it, but when I thought more about it, I think you are right. 
Maybe my associations with Mystery Train and Night on Earth were because of the same cinematographer he used on Broken Flowers. While Down by Law, Dead Man and Stranger than Paradise are still 50% Robby Mller for me. (same as Paris, Texas or Mad Dog and Glory).
In Jarmusch's films you get a real feeling for the importance of the cinematographer... Something like watching a film by Claire Denis.