Who Should Go?

Zack Wheeler will make his first major league start today which will force one pitcher from the rotation. Matt Harvey, Dillon Gee and Jon Niese have their spots wrapped up, so it comes down to Shaun Marcum vs. Jeremy Hefner.
By traditional measures you would think Marcum should be demoted to the bullpen or the minors because of his 5.43 ERA, his 0-8 record and his poor performance in his last start against the Cubs, when he could have been said to be fighting to keep his spot.
Meanwhile Hefner while nearly as bad in won-loss record at 1-6, his ERA is 3.96, and he gave up only 1 earned run in each of his last three starts. So clearly Hefner deserves to stay right? Wrong!
Here's why: Marcum's WAR is 1.4 (and he missed at least 4 early season starts), while Hefner is only 0.2, barely above replacement level.
I know some of you distrust WAR, but there are some very good reasons WAR is telling us what it is. There are 2 main things a pitcher has total control over, strikeouts and walks.
Strikeouts per 9 innings:
Marcum 7.74
Hefner 6.72


Walks per 9 innings:
Marcum 1.81
Hefner 2.76

So Marcum strikes out an extra batter per 9, and walks one fewer. It's those pesky things he can't control that are hurting him.

BABIP (batting average on balls in play)
Marcum .329
Hefner .271

So the Mets defense is turning batted balls into outs at a much higher rate for Hefner than they are with Marcum, which causes this:

FIP (Fielding-Independent Pitching)
Marcum 3.06
Hefner 4.69

So basically, because Marcum strikes out more batters, walks fewer and has been victimized by bad defense, his ERA should be close to 3, not five and a half.

Eventually you would expect those things to normalize which means Marcum is more promising for the last three months than Hefner. Especially if you consider that Marcum had four horrible starts to being the season after his injury, and has improved since.

Also throw in the fact that Hefner would likely be a more effective reliever, and Marcum would be more likely trade bait, it's almost a no-brainer to keep Marcum in the rotation and to demote Hefner to the bullpen.