So, how can we confidently discuss these as normal distributions when we can mathematically see there are skews?
They are not perfect normal distributions of course, but they are close enough.
This gets even more complicated when we introduce confounding variables. For example:
Socioeconomics: Research shows that factoring in parental education and family income virtually eliminates racial differences in MCAT scores.
Do you have a source for that?
But in any case, I do not doubt these factors would remove much of the racial distribution difference. But parental education also means that their children likely grew up in a home where their intellectual development was encouraged from an early age. And there is also a genetic component - more educated parents are also likely more intelligent and they pass their genes to their offspring. And family income is also correlated with parental education (albeit not perfectly of course).
Now, growing up in a well-off family helps with all kinds of things, and many far more directly than MCAT. Your parents might be able to hire an MCAT tutor, but you still have to do the work and take the test. Those parents can also hire a professional writer to craft the perfect personal statement and secondary essays, but in that case you don't have to do squat. So, which admission criterion do you think is more susceptible to family income/wealth?
Preparation Capacity: Total hours dedicated to test prep is a strong predictor of MCAT success, which correlates with the financial capacity to afford extra educational resources and the free time to use them.
As I said, family income helps with a lot of things. More free time also means more time to do volunteering or research, and family connections (e.g. physician parent knows the PI at a local university) can help you get a spot.
Again, family income/wealth helps with everything. But with MCAT and to a lesser degree college coursework (as term papers and such can be outsourced), the kid still has to do the work him or herself.
If you don't like the MCAT, what do you think med school admissions should be based on?