Do you only learn when you’re being graded?
As a general rule when changing complex systems, you sacrifice what you aren’t trying to optimize. If you make a random change to a car without consideration for gas mileage it’s very likely to reduce gas mileage.
(The other side of that contract is, kids are not merely attending schools to learn, but to earn a degree that carries some degree of prestige)
The OP was about students dumbing down their own work to avoid AI detectors ratting them out. That seems like a big loss.
A grade, on a single proctored test, is a crude metric, but at least it would be a brutally fair one.