Obviously I agree with the professor.
It’s pure math.
It would be better if the stats adjusted more frequently, but there is no doubt that on CPA you cannot expect to be paid more than the person deposited.
Most programs reserve the right to change you from CPA to % at any time, and ROI is the base of that too.
For affililates with high value players CPA is a bad deal anyway, and for casinos a CPA deal with an affiliate who has low value players is a bad deal too.
Personally, I dislike CPA because it seems one party or the other loses.