Well I can give you my daughter's experience that her biggest years of improvements in goal came playing on teams that were "lesser" ranked or lower tier for exactly the reasons you mentioned. The first year she was bumped up to the top team, she actually had one of her worst years of development because she would only see a couple of shots a game and the coach did not play the ball out of the back (many of the top winning A teams play kickball because they have the best athletes anyway). There just wasn't much for her to do, and when the shots finally came her way, she was far less confident and definitely not in rhythm. My theory is that around 16 it might become more important to be a keeper on a great team, but while the kid is still developing physically, being a great keeper on a decent team is a pretty good deal and will also help build confidence because the team will really appreciate him. Side note: it is ok to have your keeper play on a team that has a weak defense, but we found it was awful to play on a team that couldn't score. It's more ideal for keeper development to play with a team that can make up for any mistakes he makes by scoring once in a while. If the team can't score, every goal he lets in will feel like death. Just my .02.