There are several problems with your proposal, in addition to the one you acknowledged.
1. If the percentage of capable talmidim exceed (or even far exceed) the number of exemptions granted.
2. In Bar-Ilan University if a calculus student tried his darndest, sweating hard hours of study, and yet he gets a 55 he then flunks the course. Yet if a talmid is learning Mesechtes Brochos and he is barely finishing a Daf every two weeks despite cracking his head over the Gemora and spending 10 hours a day, 6 days a week, shteiging over it, he is an A+ student who is better suited for learning than the guy who easily finishes (and knows well) a Mesechta beiyun every other chodesh while spending half his day smoking and shmoozing. The daf every other week talmid is doing more for Klal Yisroel (protecting us) with his Limud Torah than the mesechta every other chodesh talmid. We are far better off keeping the slower talmid in the Beis Mesrash. How will any bechina account for this fact?