Dan McCutchen throws hard. Maybe too hard. That could be why he can't seem to last long enough in games to be a viable starter.
McCutchen reminds me a little of a Baltimore Orioles kid from a few years back named Adam Loewen. That 6'5'' lefty was a hard thrower who struck out nearly one batter an inning, and was basically unhittable for up to four innings. But by no later than the fifth, he would weaken, because he was tired. Beyond that, fughedaboutit.