Statistically, Detwiler and Lannan (2011) were about the same. Similar records, strikeout rates, ground ball rates, HR rates, ERA, FIP, wins, ect. The only real difference between them is their walk rate. Lannan's is higher.
Detwiler as a reliever though was a lot better. Higher strikeout rate. More velocity. Still maintained his GB rate. He would also give us another reliever that could go a couple innings if necessary and could spot start when needed.
Price
Strasburg
Gio
JZ
Lannan
Storen
Clippard
Detwiler
Garcia
Burnett
Stammen
Mattheus
Gorzo
Heck of a bullpen. Maybe the best rotation in baseball.