I DO know that Harvard (and all law schools) do blind grading; that graduating magna is top 10% of the class or better; that law review is not given out by AA (and has been heavily criticized for it -- usually only 1/3 women, and very few blacks or hispanics), and that the cutthroat law review folks don't award President on AA -- otherwise there would have been one long before him.
This doesn't mean he walks on water, but it does mean that he is no dummy, who got where is is now only by AA. Hard work, smarts (and a heck of lot of luck in his Illinois Senate race, as his formidable opponents just self-destructed one after another!!)
Your general implication, though, is a good one -- and has become very controversial among civil rights groups and educators. They are finding that most AA slots are going to: a) Caribbean blacks; b) African blacks; and c) "bi-racial" (means you've got 50% "white blood" in this generation, instead of much further back!), and a lot of folks don't like it.
The explanations for it are all highly unpalatable to the civil rights establishment. Since schools generally do choose on "merit" AMONG those they label as "black," it means that something is propelling to the top those who: a) have british educational system, immigrant work ethic, and usually tight-knit families and more religious background (Caribbeans, especially -- cf Gen. Powell); b) above plus "aristocratic ethnic" background (especially Ibo from Nigeria and some central African highlands nobility (Ugandan, kenyan. especially -- cf. Obama); and/or c) "white" ancestry and raising (often actually Asian -- cf Tiger Woods and Obama).
Obviously, none of those facts are very PC!