I saw this, and it came as a coincidence and timely too, with a discussion I had about the worth of reading/recording/valuing rotation of a pitcher in the amateur ranks. Here’s what came of that conversation.
First off, amateurs are an “if-ee” lot. They just don’t take care of themselves on a consistent basis health and nutrition wise, they don’t prioritize their daily schedules- for whatever reason(s), and their appearances can be as volatile as predicting the weather.
Second, training and coaching pitchers at the amateur level – any level, requires a lot of hands-on experience and “time-in-grade” tenure of the coach himself/herself, which is usually in short supply as it is.
Third, in order to make any finite evaluation based on rotation, or any other detail type read, one must depend on the “first off” and the “second off” big time.
At the pro level, rotation is always equated with survival. Careful attention is addressed to this – but not specifically in and of itself. Other things are addressed like grip on or off the seams, body signatures, release attitudes, etc. Then again, we’re dealing with the ideal. The ideal training facilities, training tables (diet), workout circuits, and last but not least – pitching coaches that can rely on a upstream filtering system(s) that send a works-in-progress athlete worth spending time and money on.
So, in response to this question that you pose, and it’s a good one too, I wouldn’t spend too much time on rotation as a specific. Instead, I would concentrate on diet and nutrition first and foremost, then let the pieces fall into place with conditioning and the actual coaching process of solid form and posture that address the pitching cycle (mechanics).
By the way, one of the major reasons for not having a reasonable rate of rotation on any pitch – less those pitches that deliberately stall rotation, is the thumb griping the ball too tightly, thus the ball comes out of the hand with what we call a greater “Margin of Push”. In other words, the ball comes out of the hand and plows through the atmosphere for a distance of – say, ten feet or more before the seams actually start to rotate. When the fingers of a grip are behind the ball, instead of on top of the ball, this “Margin of Push” is at it’s greatest.