I don't know how you could argue a kid well ahead of the age curve in AA and posting a 900+ OPS in his last 300 PAs as a tweener. Probably the same people who had similar things to say about Pedroia, Youk, and Lester.
The way that you can argue this is that his 900 OPS over his last 300 PAs was driven by his last 28 ABs in which he had a 400+ BABIP. In July and August he had an .860 OPS. Besides, performance in the second half in the minors can be misleading. Most of the best prospects are either in AAA or in the majors by the time August roles around. Plus 300 PAs isn't enough time for the league to figure out your weaknesses and attack them enough to materially effect your performance.
Secondly you use a bit of revisionist history to make your point. Lester for one was almost universally loved by everyone in the industry other than Dave Cameron.
In the other two examples you use two of the more unusual players in baseball.
Pedroia was a small guy with a big swing who wasn't fast or particularly athletic. Pedroia's hand eye coordination is freakish so that he's able to drive the ball often enough to be successful. Plus he's smart enough to cut down on his swing with two strikes. However most similar players will likely not be as successful as Pedroia.
Youkilis improved his strength and bat speed at an older age. NO ONE, not even the Red Sox thought he'd be as good as he is today. As you may remember, the Red Sox were willing to trade him and Shoppach to the Royals for half a season of Carlos Beltran. Fortunately, for the Red Sox, Allaird Baird turned that deal down and sent Beltran to Houston.
I'm not saying that Kalish's performance, especially in the second half isn't relevant or that those that think he's not going to start in the majors are right. However I don't think that strong performance over roughly two months in the eastern league proves very much.

