I really like the blend on Stroman's repertoire. When a guy throws a cutter, a slider, and a curveball, I think it probably f***s with the capability of the batter to pick up the spin and time the specific pitches.
If you can throw a 2 seamer, a change, a 4 seamer, cutter, slider, curve, then you've got an entire spectrum of pitches. A rainbow of speeds and breaks. You can ROYGBIV guys to death.
If you throw only three pitches, a FB, curve, and change, then you have very segregated offerings. It might be easier for hitters to pick up those pitches earlier.
Of course, having less pitches might mean mastering those specific pitches better.