I think where
Inside Shoulder is coming from is that if certain talented athletes were still in the CHS system, then there schools may be able to build a team around them.
Randwick Boys High School f'r example has provided at least two boys to this years NEW 1st XV, 1 joining in Yr 11 (yes after representing SJRU at U16 level) and one transferring a year earlier.
When those boys were at Randwick, that school didn't have a regular Rugby Team, but without them 5 other fringe rugby kids are disinclined to pull on their boots for the school and there is bugger all chance of having a team.
Moving to NEW, the boys in question undoubtably get a better rugby education, playing tougher games week in week out. The unintended consequence of the concentration of the talented athletes into only 6 schools is the collapse of footy everywhere else.