Rule 1: Do not allow players on the team unless they are true students, eligible to be in school under the same rules that a non-athlete can attend under. If you have rules for enrollment at your school normally (like # of units per term, etc., minimum GPA), they must be followed for athletes.
Rule 2: You can play College Sports for four years, with the same sort of 5th/6th rules for medical issues/redshirting, etc.
Rule 3: (I’m not even sure you need Rule 3, but maybe…) If you’ve played your sports at the Major League level, you can’t play it at the college level. Minor Leagues, Junior Hockey, anything else, that’s fine b/c it’s at or below the college level and is training.
I think that’s all you need. Real College Students pursuing real college degrees, with eligibility focused into the time span of a normal college career, and no end-of-career NFL stars coming to beat the snot out of 18 year olds.
Focus compliance on making sure these kids stay real college students. Throw out all of the concern for competitive equity and just let the market take care of that. Some schools will excel, year after year. And this will be no different than today. Some schools will undertake expensive ways to attract and retain more talented players, ranging from paying players (gasp!) to providing world-class tutoring (the nerve!), and as many books as they think their athletes can read (I know, shocking right?), and it will cost more for other schools to compete. And this too will be only slightly different from today, where that money and energy gets funneled into building palatial practice facilities and all sorts of under-the-table unseemliness.
Everything else is just the cartel working to keep its costs down.