Evan Grant has an article this morning at the DMN that delves a little deeper into the Yu Darvish situation, and examines how Darvish does versus teams whose hitters have good plate discipline.
Spoiler alert -- Darvish struggles more against those teams. And there would seem to be a certain common-sense element to that...Darvish has a high whiff rate, but a lot of that comes from fooling batters and getting them to swing at pitches out of the strike zone. If hitters lay off those pitches, Darvish finds himself more often down in the count or walking batters.
How much of this is small sample size noise and how much is a legitimate issue Darvish needs to address by adjusting how he pitches to such teams, I don't know. But the piece is worth checking out.