Skylark, what you say validates my whole argument against focusing on the changeup in h.s. It is without a doubt the most difficult pitch to command, and if you're saying the average MLB pitcher can't do it so much less so for a h.s. pitcher. My point exactly. (But you're wrong, of course, the average MLB pitch CAN command it.)
The fade, the depth, the arm speed, the count knowledge, these are things that a 17 year-old cannot comprehend. Or if they comprehend it cannot develop it against advanced hitters. So play with the change in h.s., just know that at the next level it's a different pitch.
Focus on the fastball in h.s. and develop a breaking pitch so as to get the opportunity to play at the next level. If you can't develop a hard, well-commanded fastball the other pitches are trickery meant for J.C. ball.
(Nothing against J.C. ball, it serves it's purposes. Generally for pitchers to develop more velocity, a quality breaking pitch, academics or a combination of these factors.)
Once you're 20+ the nuances of the changeup (your current B.P. fastball) will be revealed.