The problem is that graduate school admissions committees are left with very few quantitative measures. Undergrad grades are difficult to compare, because every university grades differently, and applicants come from different countries with completely different grading scales. So many people score perfectly on the quantitative GRE that it's nearly useless. The verbal GRE seems irrelevant to a scientific field, and it seems pointless to rule out international applicants because they don't know the meaning of the word "garrulous." In short, the subject GRE was one of the only uniform quantitative measures available to admissions committees, and now it's considered "racist."
There upshot, ironically, is that the elimination of quantitative measures makes discrimination easier to hide. This discrimination is meant to be positive, helping increase representation of underrepresented groups. The applicants who suffer most from this policy are those who are just on the line between admission and rejection, and who don't come from the "correct" demographic. The people pushing these policies think they're changing the world for the better, but it sure looks unfair to the individuals they're denying entry to. Applicants are being treated as representatives of their race or gender, rather than as individuals who should be considered individually.
It's fairly easy to spot the "heavy-hitters" just from recommendations, undergraduate publication record, thesis, and GPA. In short, MIT and its elite cohort (CMU, Caltech, etc.) only accept undergrads who found their way into their professor's research groups -- this feat in and of itself is a superior indicator.
Undergrad research (including a published first-author paper) is almost a requirement now for entry into many top programs. But you have to know the research group the student worked with, and you get applications from all over the world.
The subject GRE is a uniform quantitative baseline. It isn't everything (or even most of everything), but it is a somewhat objective standard that can at least flag applicants who might have real difficulty in a top program.
The thing is, I've heard "equity" arguments for disregarding not only the subject GRE, but also published research ("Not everyone has the opportunity to do research as an undergrad") and letters of reference ("Letter writers suffer from implicit bias"). The "equity" advocates seem to want to throw out every piece of relevant information. Of course, that makes it easier to hit whatever targets "equity" requires.
Having been an undergrad at one of the above, I can assure you both are super impressive (in either STEM or humanities), and should garner special attention from graduate programs.
> The subject GRE is a uniform quantitative baseline.
It seems we've moved off the topic of undergraduate acceptances to elite graduate admissions. The dearth of slots at these rarefied levels relative to the global supply of smart people is such that results from an arbitrary exam coming out of New Jersey would only get a second look in the narrowest of "splitting hairs" cases.
They're both great institutions, but the grades from one are much less meaningful than the grades from the other.
Harvard et al can now pick from a wider pool and still claim they have the "best and brightest".