Fenway touches on one of the best life lessons we can all learn and live by. Control what you can control. This will be a lifesaver in baseball and in life. The best way to navigate the politics (and there will be some at all ages) is to be better than the politics. Encourage your child to work so hard, get so good, that these things don't even touch him. If he's not getting what he needs from his coaches find new coaches (with a new team) or, if he can't switch because it's high school, additional coaches (private lessons on the side).
My best advice as a parent, because I've seen it so many times, DO NOT participate in victim blaming with your child. I've watched PARENTS kill their child's love of the game by complaining about politics and perceived slights. It impacts how the child plays and is usually a self-fulfilling prophecy. If your child is venting to you, tell them you hear them and then ask, "now what should we do?" Hopefully their answer is "go to the cage to hit" or whatever is needed to get the player to the next level. Support that.
Good luck