I know what you are saying, just find it difficult and unreasonable to expect Sanchez to be able to master 2 additional pitches. He has the cutter which I think was developed for the reason you mention. I think the priority should be command and not learning a slider as that is what is going to make him the most effective. Was weird, last year
Sanchez actually got more whiffs as a starter compared to a reliever so I think throwing the curveball more will get a few more whiffs just be virtue of the hitter thinking about it.