Hang in there. Hopefully, he will get his chance and be able to prove himself.
My son faced a similar situation last year. His freshman year, he was a starter on varsity. Pitched 4 complete games and did well. Sophomore year, new coach. In the first game, starter went the first 3 innings, my son came in for 4,5,6. Gave up one hit, no runs and got out of a bases loaded no out jam in the 6th in 0-0 tie. Coach decided he wanted him as a closer because he could get out of jams and not fold. Fast forward to one of the 1st games of the season. Starter goes 1 1/3 innings giving up 5 earned runs. Son comes in and finishes the last 4 2/3's giving up 1 hit, 1 run and has 7 K's. From that point on, he is back to being a starter.
Bottom line is, you have to do what the team needs you for. Keep yourself ready and in a position where the coach can't help but use you as a starter. If the oportunity presents itself, be ready and hope that the coach sees the light. Until then, let the coach know what you would like to do, but do what the team needs of you.