How much a hitter dreads a pitchers off speed stuff is directly related to how hard he throws , how much movement his fastball has and how well he can locate his heater. It all relates to the most important pitch a pitcher has and that is his fastball.
In hs a pitcher with a dominant fastball gets hurt often when using the cu. All he does is speed up the batters bat and allows them to do damage. The good hs hitters dread the cu because it slows down their bats and allows the pitcher to get his fastball by them. Without a fastball that can command the respect of the hitter the cu is not nearly as effective.
The best pitch in baseball has been , is and always will be a well located dominate fastball with some movement.