Pretty much every other top tier school gives out merit to URMs. JHU, Harvard, Columbia, Yale etc. This is why URMs go there.
@Asperphys URMs do finance scholarships but they finance them at the schools they went to (not Wash U).
I'll answer some of your concerns.
Giving
preferential aid to URMs (is this really what Penn does??) might work, but given WashUs high tuition, this might be viewed as kinda discriminatory against non-URMs.
As I stated before, many schools give merit to URMs and the world hasn't ended. JHU, Harvard, Yale, Columbia, Sinai etc. These scholarships are not specifically for students of color, but since disadvantaged students are more likely to be a student of color, these scholarships attract URMs.
For example, how important is it for URM students to have URM faculty as mentors? Do they really feel that non-URM faculty cannot relate with them or would be unsupportive?
It is absolutely important to have URM faculty has mentors. non-URMs have trouble with this but just imagine if you were a White or Asian student and your school only had one White or Asian surgeon. It would be weird right? URM faculty are important because they understand how to get to where they are as a URM. Medicine is a very different culture, language, and lifestyle for some and having a URM faculty mentor helps. Second, the number of URM faculty is a proxy for the culture the school provides for URMs as a whole. So, the number of URM faculty is good in itself, even if I wasn't going to work with with one. Also this is the most important. How open is the school as a whole to diversity. How much non-URM faculty are committed to diversity. Some schools make it clear that they are. Some don't. Diversity and inclusiveness means that the administration is invested in the mission and believes it helps everyone. I think people on SDN don't understand this and thats okay.
When URMs look at the number of URM faculty we're not saying "We only want to be educated my URM faculty". That's silly. Being a URM doesn't make you a better faculty member. We're saying "Oh, this school has URM faculty. Cool, I will be supported by all faculty because there is a precedent of educating and supporting people like me" Of course this isn't always the case, but this is the ideal.