There is no way to prove this, but my opinion is that good Major League players are going to be good Major League Players. Evan Longoria spent very little time in the minors. Beckham didn't spend a full season down there. I'm not saying that every quality major league player would have been the player they are if they had gone straight to the bigs, but I fail to see proof that Borchard, Wright, Anderson et al. would have lived up to the hype had they spent more time in the minors. Borchard couldn't hit a Major League curveball. He wasn't going to learn how to do that in AA. Dan Wright had electric stuff, but I see no reason why he wouldn't have blown his arm out regardless of where he was.
Sometimes there is no pattern of correlation and causation. That's just my opinion, and until we can see into alternate pasts this debate will remain completely subjective. Just my