The Departed is great, but it is a remake that closely follows the original, especially in the first half of the story. That's why I wouldn't put it top level Scorsese. The story beats were already pre-established by another. Same with Cape Fear
I do think of Insomnia as a less impressive Nolan movie because Nolan usually writes his own original ideas, even with Batman. But Scorsese rarely does so, so a director who usually works from other people's script making a remake is not that different, especially since he puts his own flair in those films and they depart (no pun intended) from the original films and aren't just a Quarantine or Let Me In (which are mostly redubbed versions of the originals).