Ultimately, you ask the student, in one audited test, to demonstrate that they've absorbed the essence of the course material and have developed some level of mastery.
If the change is not designed to educate the student, then the point isn’t education.
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.
Schools are not merely in the business of maximizing education, they have their own prestige to uphold, and they would like to give degrees with their name on it to students who have actually upheld their end of the contract.
(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)
To what end? Not cheating on the weekly assignments is surely more beneficial to learning than cheating on them is, but I don’t see how removing the assignments altogether would help students learn.
It's a crude blade to avoid the issues of AI pollution of weekly submissions, of which few teachers have much confidence that the submission itself was actually written by the student - who's assumed to be learning something.
The OP was about students dumbing down their own work to avoid AI detectors ratting them out. That seems like a big loss.
And what would the goal of that be? I thought the goal of education was... education. The grading is not goal in itself. Will this really motivate kids to do better?
It's to prove that a student is actually educated and has a firm grasp of the course material. If one gets an A every week on AI-assisted submissions, can one make such a claim? And can a teacher make the claim that they've achieved any actual education of the student?
A grade, on a single proctored test, is a crude metric, but at least it would be a brutally fair one.