Interesting thread.
To me, perhaps the rating system ought to be personal to a particular coach's style. For example, a coach who likes to see deep counts, moving runners, and more of a small-ball approach, that coach may reward higher quality-at-bat points to those hitting attributes so-produced from his players. For a coach who likes more of the power game, he might reward a kid more points if he hits the ball hard regardless of whether he worked the pitcher deep in the count, for example. In other words, that particular coach is coaching for power rather than finess and he rewards his players accordingly (e.g., his quality-at-bat ratings rewards hard hit balls higher than moving runners or working deep counts). I don't know if that makes any sense, but I don't see any reason why there would necessarily be a universal quality-at-bat scoring system out there. I could also see a coach having multiple scoring systems. He might have one system for a power hitting first basebaseman and a different scoring system for a line-drive hitting second baseman whose primary job was to score runs or set-up run scoring opportunities rather than driving them in.