I would look at the positives of this situation. If he is one of only two Freshman on the team, that means the coaches were very selective this year and must really like him.
If there are only two Freshman on the team, that implies there are a lot of upperclassmen returning or transferring in. They are naturally going to get more chances and more reps. They too probably get few opportunities as Freshmen and now is their chance.
If he is a part of class of two, he is going to get great leadership opportunities in his junior and senior year. Becoming a leader or captain are incredibly valuable life skills that will serve him beyond college baseball.
Finally, as others said, there is a big difference between 18 and 22 year olds, just as there was with 18 year olds and 14 year olds. Every now and then there will be a phenom like Rocker burst out as a Freshman, but college baseball is really hard. Freshman have to learn so much and build up their strength and understanding of the game. It takes time and a kid has to earn opportunities over time.
Hopefully you and your son will be patient and let it play out over the coming years.