Caruana is very good, but seems unpredictable. He had a fantastic result in St. Louis and has shown he's capable of being the best (for one tournament, anyway), but he seems to have some mediocre results too. If I remember correctly, last candidates I think he didn't deal with the pressure well.
Caruana did not qualify for the last candidates tournament.


All this is off the top of my head so it might be completely wrong, but here's my thoughts: