I just looked over the past 10 years' voting and it turns out that between the 2 leagues, only 3 guys have won a Cy with an ERA+ below 150 (R.A. Dickey, C.C. Sabathia, and Max Scherzer). Nobody in the AL had an ERA+ of 150 or better this year. CC's was back in 2007, but the two guys who have done it more recently had big K numbers, 20+ wins, and a sub-3 ERA. Nobody in the AL this year comes close to that across-the-board profile. I still suspect that Porcello will win. If I got a vote I might be tempted to list Britton at #1. The Cy Young is not necessarily a "Most Valuable Pitcher" award. Obviously the top starters all put up massively more "value" than an elite reliever. But Britton was clearly the most exceptional pitcher. None of the starters really stand out - there are about 8-10 guys with similar resumes, and none of them really stand out. It's one thing if you had a hard time last year differentiating between Arrieta, Greinke, and Kershaw. They were all obviously incredible. The top pitchers in the AL this season were what most people would probably call "pretty good." Britton was extraordinary.
Not only was Britton's 827 ERA+ the best in history, it's only the 3rd season of 50+ IP in history above 600 (2012 Rodney, 1990 Eck). I don't actually necessarily think it was clearly the greatest relief season in history. ERA/ERA+ are clearly the most important pitching stats by a wide margin. I think most people on here know I don't buy into FIP. But sample sizes for closers are generally pretty small, and luck does play a bigger role. Britton's K rate was unexceptional enough, in elite relief season terms, to leave a valid debate against, for example, that 1990 Eckersley season, or Gagne's perfect season in 2003, or Kimbrel's great year in 2012. But it's pretty clearly one of the greatest relief seasons we've seen, and weighed against the sea of mediocrity in the starting pitching field, I can see where it could be good enough to garner a lot of votes.