The fact is that most of the parents that complain about the holdbacks say it's about safety but in reality it's about the older kids dominating on the field and getting the better recruiting options.
Just be honest and say that you don't like older kids taking away precious D1 spots from your kid.
Your truly do not get it. It is not about the D1 spots (although I suspect it is for you). It is about showing up at a tournament with kids 11 to 13 years old and playing in brackets with kids 14 and 15 year olds. Not so bad for the 13 year old playing against a 14 year old, but quite a problem when the 15 year old goes after the 11 year old in a game setting. When that happens it is not a game, but a bad and dangerous (yes dangerous) farce.