I remember Palmer talking about Scott McGregor, and how the O's wouldn't let him throw his change up in the minors because it was too good. I guess nobody does things like that any more.
Some groups will. Matusz and his CH. Bundy and his Cutter. There have been pitchers that we have handicapped in the minors with the theory to make them get better with their other pitches and not rely on their overpowering ones.
However, this also screws up a lot of pitchers, changing what got them to the big leagues and making them do things your way. The whole square peg in round hole thing.