from my understanding this age group wasnt soley picked as an A and B team.Kids were split up to even out positions and expose some to different coaching.i wont argue that there is a substantial difference between the squads though.as for kids walking away from the game,lets be real.kids in these age groups are swapping clubs because they feel they can play with better teammates elsewhere already anyway.sadly,making kids play with kids who are not as good creates just as many issues as it solves.even your club picked an A and B team in 11's except instead of playing them they kicked the B kids out altogether( i know the reason why but the results were the same).The idea of playing kids in A and B then putting all the A teams together also has merit but then do the B team kids ever get the chance to catch up.Theres no right or wrong path,but im seeing the consequences of all the methods and no one has it right.im personally of the opinion of giving as many kids access to the program and hoping it creates a really big talent pool at 13 for the kids to take the next step in their development across all the NPL clubs.kids that arent standouts in SAP might be better suited to the bigger field, more space etc.if they have the fundamentals correct at that age (dribbling, touch, shooting) the next step might be where they thrive.
on a side note i was watching u/11 Olympic vs Jets girls just before the Jaffas game you were referencing. The jets keeper was doing the exact same thing, standing on half way all game.obviously its a club coaching philosophy and was interesting to watch.