In Chapter 7 of The Book, Tom Tango, Mitchel Lichtman, and Andy Dolphin discuss starting pitchers. One section deals with the question of whether a pitcher should start or relieve.
It stands to reason then that you put your better pitchers, on average, in the starting rotation. We can go through each team and we’d find this to be true. While you might have one team with an Eric Gagne or Trevor Hoffman, and so the #1 reliever is better than the #1 starter, it is more likely that the #1 reliever falls in somewhere among the top two starters.
Having experienced both the Gagne era and Hoffman era in Milwaukee, it can be hard to imagine a time when this statement was true.
Of course, when The Book was written, in the early parts of the 2000s, these players were truly dominant pitchers. Gagne had a crazy 1.14 xFIP in 2003 and may have been the most dominant pitcher against right handed batters of all time. We saw Hoffman pitch like a Hall of Famer just last season.
I recommend that everybody who reads this site also reads The Book. It completely changed the way that I look at baseball and offers some great insights to the game, even if it is a bit on the heavy side. Check it out if you’re at all interested in sabermetrics.