Any pitcher who wants to play at the highest level must have a competent down ball! It is the one pitch you can leave a full ball on the plate and not get hammered every time. If your only down ball is a change up you will struggle with a hitter that actually reads the spin. That pitch is NOT a change up, it is just a slow pitch with 6-12 spin that a good hitter will square up. Despite your current success as you move up you cannot use a down ball change up to setup the rise or vice versa. Your change up should look like another one of your pitches in terms of spin and spot. Learn to throw a hard drop. That along with a good downward change and rise is a setup for long term success.