Because the marathon is run so much less frequently than other races, it is hard to know when one bad race will spiral into the end of one's competitive career.
I would agree with Kimetto's Chicago CR being as impressive as the WR. But that was almost a whole year ago. I don't think a bad race at Boston means he is "done" as Letsrunners like to say, but he hasn't exactly had a lot of reason to think he is ready to duplicate 2013 other than him saying he is ready to roll.
That's why I'm picking him to win but not get the WR.