Welcome to the hsbbweb BlueRidgeBandit!
This topic comes up here often on the hsbbweb. Many parents feel their kids will not be used or developed properly by the high school coach. Sometimes you have to put yourselves into the shoes of other players, coaches, and parents however. Every moment yours is developing some skill out on the mound, someone elses is sitting and watching.
Perhaps the best thing a high school player can develop is the tenacity and pereverance to work on his own deficiencies while waiting for the opportunity to perform. The way a player is used is not up to the player or worries of his parents however. Let that burden go. Encourage him no matter what the role. Encourage him to be mentally tough to perform when called and to never hang his head.
Focus on those things that are in his control rather than things that are not. Coaching decisions are out of his control no matter how much worrying a parent may do or how many strings parents think they are pulling behind the scenes.
Encourage your son to develop his abilities, be the hardest worker, be the best teammate, and let the chips fall where they may. Even if they use him in the relief role, if he has the proper arttitude, you might be surprised how much the relief experience will help him in the future. Most college pitchers start their careers as relievers so it is a good skill to develop.