Quick question: Can anyone name a successful major leaguer who ever had a full minor-league season like the one Evan Chambers is having? Chambers is currently hitting .217 AVG /.405 OBP /.337 SLG. He isn't quite a standard Moneyball sort of draftee, in that he wasn't picked out of a four-year college and seems to have at least some defensive ability, but he reminds me of the sorts of players the A's and Blue Jays liked to pick in the early aughts. Obviously, he can control the strike zone, but it isn't clear whether he has any hitting skills beyond that.
Which is too bad, because the whole "please walk me" thing won't fly at the higher levels, where pitchers who can throw strikes will happily do so until Chambers gets the bat off his shoulder and shows he can do something with it. Many players in the low minors can improve their plate discipline somewhat as they age if they can hit for average and power, but I don't think it works the other way around, which is why Jeremy Brown never made it as a major leaguer and the Moneyball philosophy of drafting polished college hitters who take walks above all else was basically bunk.
By the way, the most similar minor league hitter to Chambers I could think of off the top of my head (and I'm sure there's some much more obvious example from the Pirates system, but I can't think of one) is Brian Jeroloman, a catcher with a career .241/.372/.338 line. The Blue Jays, who in the J.P. Ricciardi era adopted all the Moneyball ideas except the ones that actually made sense, picked Jeroloman out of the University of Florida in the 6th round in 2006. He posted a .421 OBP in 2007 as a 22-year-old in the Florida State League, but he's mostly been stuck in Class AA since then. He hit very poorly there last year but has played well there this year so far as a 25-year-old. He's now somewhere between a very, very fringy prospect and an organizational player. Chambers is still young, so there's hope, but his performance so far this year is actually about as bleak as a .400 OBP can possibly be.