100% agree. They will all catch up in HS. Some of our team's smaller players are the mightiest and most aggressive. Our biggest player was let go was slow and timid. A kid who was small and a defender came to our team before tournament season and oh my, he was RELENTLESS! Our big soft guy was intimidating at first glance on field but when game started, it was our mighty mouse who made players go horizontal and frustrated. Please contact coaches or directors of teams you have interest in. Good organizations will walk you through this thought process and talk to you about their team's needs.
Tell your son to keep practicing and strength train. He will be good!