Same argument was made after last year that FIP/BABIP would lead to Detwiler falling off(I was one of his staunch defenders over the offseason). Just checked Fangraphs and his FIP has actually improved by .62 and his K/9 and BB/9 rates have both improved.
Maybe he drops off, but I think the guy at some point becomes better than his advanced number would indicate. ERA has stood the test of time for a reason.
I hate the idea that somehow sabermetrics make what actually happened irrelevant. It's just simply wrong. Take John Lannan who has significantly outperformed both his FIP and xFIP over the course of his career. In a sample size of 764 IP John Lannan has a 3.99 ERA with a 4.60 FIP and 4.46 xFIP. If FIP and xFIP were accurate these numbers should be much closer to equal after such a large sample size but they are way off. The reason for this is that while FIP and xFIP are great indicators of future success in general they just simply can't account for all the on-field factors that numbers alone cannot reflect. Numbers tell you a lot in baseball but they simply don't tell you the whole story. At the end of the day you should always put more stock in what actually happened then what we think should have happened in theory. What actually happened has the benefit of not relying on human error and the (inevitable) inaccuracies that sabermetrics present by putting everyone on an equal numerical scale when they obviously are not pitching the same way. Sabermetrics are often great predictors but that is all they are. At the end of the day a player's value is determined by what they ACTUALLY DO. And Detwiler has been a stud.