First of all, congradulation to you and your son! Only excellent player gets this type of treatment. LOVE to see 小中男 like yours!
It is VERY common in recreational baseball league. Just google "daddy ball". But does not seems like you are in a club. Normally daddy ball is less common in club teams. Your club seems more like rec. team. Normally, the only goal of some daddy coaches is getting his son to pitch. Looks like the coach of your team is already sold to that coach.
Typically, they will only bench the kid. And you can do nothing about it. Maybe you can pressure the club, depending on how much you know about the politics behind and how active the parents are in the team. But sometimes, they will do more, depends. Then you have to do something. Really pay attention to what they do.
Two cents:
1. Try to stay in the team until the seaon is done. And let your coach know you aware the situation and not happy. At the same time, start to look for other options, clubs in other cities that is more fair...
2. Keep in mind, maybe you don't care about how well you son plays. If he learns how to deal with this kind of situatiion, it will help him A LOT in the future... Sometimes, daddy and mommy have to know how to deal with it first...