Progression is driven by multiple things. Stats are among those. Players grow faster in AA than AAA because they gave weaker competition. I have always used my AAA for my career minor leaguers and sometimes for overflow if I am overloaded at a position.
Players on average increase by 3-5 overall per year. It can be more and it can be less based on multiple factors like I said above. Sometimes they just randomly grow slow and are "busts."
I also do extensive edits to draft classes. That is another factor here and something I seem essential to long term franchise growth so my experiences do differ at times.
I've always done the same. My top prospects stay in AA until they're ready to jump to the pros. AAA is basically for guys that are just fillers or part time fill in guys.