The important thing to keep in mind is that measures damage when that particular pitch is thrown. So if the Cubs lay off curve balls out of the zone and then hammer fastballs, that's not reflected. Eyeballing the game logs of the highest curveball users, I don't see much sustained success. There's a couple guys that had one good start against the Cubs(Pomeranz, Koehler, Moore), a few that the Cubs dominated(Wainwright) and mostly guys who gave up 3 runs in 5-6 innings(Gio Gonzalez, Quintana, Eickhoff).