[KBLover]

I've never done a formal study (don't have the energy or even a good methodology), but from what I can tell both in my leagues and the OOTP23 online league I'm in:

Pitchers:
Usually Stuff unless they have a high GB rate. Then both Stuff/Movement can move in lock step and if velo/pitches are low, Movement takes the lead.

Pitchers with poor pitch ratings, even with high potential, can take FOREVER to move their stuff up, especially if it's bad third-fifth pitches (and by that I mean their rating, not the tradition 1 = fastball...if fastball is the 4th rated pitch, even with high pot it can be slow and hold the Stuff rating back accordingly.

Control - if it's bad, it's another one that can take forever to develop. If it's around 35-40, it probably will move up gradually, perhaps faster with a Finesse pitching coach (don't quote me on that, but just something I do - switch out pitching coach at all levels to Finesse if there's prospects that are good...except for 20/60 control). It seems like Control is the "failed prospect" rating. Guys that have 50/60/70 in Stuff/Movement but...20 control....and get stuck there. They either are effectively wild (maybe, one guy in my league is 80/70/20 and he's been a journeyman hit-or-miss guy) or just wash out and eventually quit in the minors.


Batters:
Seems like it depends on how much they start with. I don't know if that sets some kind of "archetype" development in the engine...but those Joey Gallos rarely develop good contact even with plus potential for the league. I've seen these guys with 75 power and maybe go from 25 to 35 in contact.

Power tends to "catch up" better (i.e 70 contact with 20 power is more likely to maybe reach average or fringe power more likely than 20 contact and 70 power will reach fringe contact).