Duncan has one way to "fix" a pitcher and it only works on certain types of pitchers. He teaches them a sinking fastball and orders them to pound the strike zone with it. They get less K's, but more GO and much less FO and HR's.
This can transform a guy with a good arm who never was able to put it together, like Carpenter, Looper, Weaver, Suppan, Lohse Wellemeyer, or Pineiro into a solid starter. But it doesn't seem to work as well with young pitchers. Matt Morris was the last homegrown Cardinal to make it in the starting rotation. Maybe Duncan needs a gut to be desperate in order make him change.
Not saying it's a bad thing, just explaining how it seems to work, in my opinion.