If, at age 22, a player can't make consistent contact against FSL pitching, he's a huge, huge longshot to pan out at all. I'm not familiar with a single example.
*Joey Votto hit .256 his year in FSL with 17 HR and 83 RBI.
Top player for Cincinatti Reds
*Matt Kemp hit .306 his year in FSL with 27 HR and 90 RBI.
Arguably one of the Top players in MLB before injuries
*Marcell Ozuna hit .266 his year in FSL with 24 HR and 95 RBI.
Now starts with Marlins after playing in FSL in 2012
*Javier Baez hit .274 his year in FSL with 17 HR and 57 RBI (half season)
Top 5 prospect in all of minor league baseball.
Kennys Vargas hit .267 las year in FSL with 19 HR and 93 RBI
Now everyone is in love with him (rightfully so) because he was hitting over .300 this year and producing at the same pace.
Low batting averages do not neccesarily mean poor production, but it does mean poor contact. These guys are all successful because they produced results in their careers, not just average. If you are judging based on the success of a Matt Kemp then you are being unrealistic, because every prospect can't be considered amongst the best to play the game. Most are hoping to be solid (good) MLB players.