HBD isn't predictive; it's a null hypothesis. The predictive claim is the inverse: that there aren't substantial ability differences between racial groups. Unfortunately you do have to mention race because that's the claim that people are making; obviously the group of MIT students has a different mean IQ from the general population. So differences in outcome are because of different starting conditions, racism, or culture.

In particular, a belief in ~HBD means that, when black kids don't get into Harvard at population-representational rates, the system is unfair SOMEWHERE. Maybe it's a problem with lousy schools, maybe there's racism in college admissions, maybe it's generational poverty. But, as a society that values fairness, we have a duty to figure out what's going wrong and try to fix it.

With ~HBD, the system is unfair and we have a duty to fix it. With HBD, the way things are might be fair and something like affirmative action might actually be unjust. That doesn't mean they necessarily are fair--just because groups can be different doesn't preclude racism--just that they aren't automatically unfair.