I think CHSAA's rule is a good rule as far as it goes--one year of sub-varsity-only eligibility for those who transfer during high school. What's important about football, cross country, and track, though, is that the school season is still the main season--probably basketball and wrestling, too. As long as NXN doesn't come in and blow things to pieces for a few athletes who have the potential of tipping the scales and making their new team an NXN team, the one-year-of-sub-varsity-eligibility is a reasonable deterrent for cross country (and therefore, at least to an extent, track).
With sprints and jumps, though, the kids who are inclined to move around are more or less coming in to wherever their club coach coaches as freshmen. See below for at least a partial fix on that situation. Throws seems relatively unimpacted by the whole club/transfer scene.
Football is clearly impacted, at least in large metro areas, by top kids coming in as freshmen to local powerhouse programs. Schools like Cherry Creek, Pine Creek, and Pomona have been getting the top kids for a long time now. And, of course, Valor. Mullen used to, but the big scandal they had hit them hard and they're more or less out of the picture of state titles now.
One substantial solution would be to hit schools with a proportionality in their enrollment count. For every kid coming in across an attendance boundary (or, say, starting with grade seven for private schools and charters--except that some private schools are just high schools) your enrollment count actually goes up by a multiplier. So, if one in 15 kids in your school goes out for football, each transfer from across the boundary (or late into your feeder/middle school) counts for 15 against your enrollment for that sport only.
That way, pretty soon you'd have all the magnet football schools in one classification--where maybe they belong. Same with volleyball. Same with cross country. And parents wouldn't be nearly so anxious to talk to other parents to bring more new kids in across lines--at least not until they're past a certain threshold where it doesn't matter much any longer, anyway.
In at least a partial nod to Valor, they went 5A in every sport a couple years back even though that's not where their enrollment is. They said they were willing to play in Colorado's largest classification in every sport. That, at least, acknowledges a certain reality that Lutheran and Mullen haven't acknowledged yet. Regis is also in Colorado's largest classification in every sport.
We could discuss whether state athletic titles are the main thing Jesus wanted Christian schools to accomplish, but to little avail. It's clearly the leading draw for at least certain Christian schools and certain parents.
I suspect that data placing 5-9.5 at the top percentile of girls heights is a little out of date, but your point still stands about Chaparral volleyball.