I agree with your point about the Demise of SBHS and I agree that it definitely got pushed down the hill faster by the DET.
I would say it's hard to have a go at a sport high school about not introducing anyone to a new sport. You assume most students have enrolled at the sports high because they are considered talented at a specific sport already. It would be rare to adopt a new activity when you are already identified in another.
If I recall correctly. Will Skelton was suggested to play Rugby whilst at a sports high by the Rugby League coaches.
Rugby Australia should be talent Identifying kids that may suit the sport.
But that is the reality of it though. The kids who go to sports high schools learned their game and continue to have it developed by the sports themselves and the schools contribute little to their development (Westfields the exception).
We can always find exceptions to that (happy to accept Sketlon as one) but they are exceptions and definitely not the rule.
When you also consider that none of them appear in the HSC top 150 ranks, their reason for existence is unknown.
Develop your sport? Nope - the sports themselves do that
Develop your education? Nope - no evidence to support that either