You leave out heavier kids, what about heavy kids who are late bloomers? Which was me, I was unable to play because I weighed too much from 6th grade on, and was in no way good enough to play up with older kids. So I wanted to play, and eventually tried in 9th grade, but got killed because your system "didn't keep this kid in the game", but I persisted and eventually played varsity through 12th grade, but not playing early put me way behind. Truth be told, some of the kids that where thought to be better players in middle school, I beat out eventually, and by 12th grade, they where long gone, so I guess by the end I prevailed, but I'm certain I would have been better had I not been discriminated against by the system early on. In all honesty, the idea that bigger kids will hurt the smaller kids is BS, a lot of the bigger kids are slower and less athletic, they're not all studs. I was soft and fat, and I grew taller and started lifting weights after 9th grade and got in shape, but 5th-9th grade I was FAT, WEAK, and SLOW. If I could have been playing, I would of gotten in shape sooner.In my experience which was running a youth program for ten years, and having kids who played football from 5 it's a good system and it works.
What you find is a lot of "little kids" the larger numbers in youth football, are late bloomers size wise and many become big strong kids in HS.
Lot's of "big kids" are early bloomers and and growth slows down and the so called "little kids" catch up and pass many of the "big kids" in HS.
The objective is to keep all the kids in the game until they get to MS/HS freshman where they all mix together and growth starts to evern out. They start lifting weights around that time which becomes a major factor as to who succeeds and who doesn't.
The truth is most communities don't have the numbers of "big kids" to keep a youth program going.
Both of our kids were so called "little kids" in youth football but were two of the biggest and strongest kids in the football weight room in HS.
The system works, it's been in place forever and won't change much!