This is a scouting/coaching issue, not an issue with who develops when. If a scout or coach can’t see a kid is never going to be a good player when others catch up physically, or a smaller kid is going to be a good player when he catches up physically, they suck. Having a U16 age group isn’t going to solve that. Until scouts and coaches know what they are looking at it will be status quo.
I agree that this is primarily a scouting/coaching issue, but a separate U16 age group can help mitigate that by keeping kids who have recently grown and "caught up" physically (or are still in the process of doing so) in the mix and in sight of these scouts and coaches who cannot otherwise seem to project ahead and can only see what is right in front of them.