I would think a Shift helps a hitter. Tells him how Pitcher is going to Pitch him. Almost like stealing signs. The Defense is on Left side, so you know the Pitcher wants the inner half of the plate, it don't matter Fastball or Curveball, the Pitcher has to throw the ball to utilize the Defense. Hitters not thinking today, and smart hitter would hit Pitchers mistakes, which would be outer half of plate, where there is no Defense. Eventually some smart hitting Coach will see, hitting to all Fields makes you a better hitter all around. Not just because of Defense, it makes hitters better. Pitchers can't pitch you one way.
If all you are is a one dimensional hitter (pull hitter), your really not that good of a hitter anyway. Mostly stupid, too.