Interesting post. This is hypothetical for me. If your son's passion and dream is to play in the MLB then why not pursue that with abandon, and not doubt it. If your son is healthy that is a lot of it. I have a neighbor's son who played in the MLB and AAA (back and forth) for a few years after a great college career. This year he wasn't re-signed by that MLB team, so he's headed overseas to play in Asia because he wants to continue that professional dream. Instead of asking why, it should be why not if that is what he wants to do. After talking to him over a few beers a couple years ago, he told me there is a lot of luck involved as well. I understood that to be that you have to be healthy, put yourself in a position to be lucky, then be lucky to play baseball professionally.
As always, JMO.