The idea of a salary cap at either the NIL level or coach's salary level is a concept that does not apply to college athletics. The purpose of the salary cap Is not to ensure parity (though parity is an offshoot and what owners want you to focus on). The purpose is to protect profitability by removing the prisoner's dilema from consideration. No owner can attempt to win just by outspending the other owners. It is meant to protect the owners from themselves through colluding to keep costs down. It only works because all parties agree to it. All parties agree because they get compensated for their agreement. Owners through revenue sharing of national TV contracts. Players through mandatory minimum spending by owners.
In college sports there are no owners, there is no revenue sharing, and there are no collective bargaining units. The NCAA does not/cannot control an athlete's NIL earnings. And they never will. Telling athletes what they can earn (zero) is what got them in this predicament in the first place.
On top of that, the NCAA has gone to court repeatedly to argue athletes are not employees. How then could they argue to have a say in an athlete's earnings?
As for coaches, there is no single authority like the MLB, NFL, etc. that could attempt to normalize compensation across schools or sports. And even if there was, take note that none of the leagues with athlete salary caps have coach salary caps.