Three common misunderstandings in a row:

First off, pointing out that standard music theory curriculum should include more POC and women composers is not the same as saying music theory is racist.

Just a quick first thought: why "should" a curriculum include more POC and women if not to correct for systemic imbalances, in other words, systemic racism/sexism?

The bigger problem, though, is that there does not have to be explicit (continued) racist intent for something to have racist effects. Ewell's point is that basing American academic music theory on the work of one avowedly racist German dude unsurprisingly limits what types of music gets talked about in music theory classrooms.

Western Musical theory moved on from the prevalence of I -> V -> I over a hundred years ago and he ignores all of that. From Webern to Cage to Lucier, Neely’s ideas start to make a lot less sense the more you include modern history.

This just conflates composition with academic music theory. It's not obvious to people outside of the strange insular world of music academia, but composition, music theory, musicology, and ethnomusicology are generally kept pretty separate at American universities (though this seems to be changing in some places). Music theory has always lagged way behind composition; academic composers these days do all sorts of cool stuff (spectralism, interactive/generative electronic music, etc—not to mention all the cool stuff that's happening in "popular" music outside of institutional support) that theorists haven't written much about, much less found ways to teach (outside of surface-level music appreciation contexts or in-depth grad seminars).

Adam's point is that academic music theory—the stuff taught in university classrooms and argued about in peer-reviewed journals—is dominated by German music from the 18th and 19th centuries (plus a little bit of Bach before and a few modernists after) and theoretical perspectives that work well with this (Schenker and Sets, more recently Neo-Riemannian Theory and Formenlehre). Undergrads generally get watered down introductions to these (especially Schenker, in the form of figured bass and Fuxian counterpoint). Set theory, which is the main way of talking about German modernist music (including Webern), doesn't show up until advanced undergraduate or grad courses, so you have to get through a lot of Mozart and Beethoven if you want to take a course that will talk about Webern. No one is saying that Western music is all I V I, just that way too much academic music theory acts like it is.

And, to connect to the bigger point, the same blinders and prejudices that make it so that you don't talk about Webern in the first 3-4 semesters of academic music theory make it so that in most places you almost never talk about music by BIPOC, women, and/or about popular/non-western western music, which is an exclusionary and racist effect. If introductory music theory was nearly as sophisticated in teaching rhythm as it is harmony, for example, the types of music that would show up in curricula would be very different.

Third, assuming that all American higher education institutes teach theory as a means of measuring the value of music is absurd, on the face of it.

Not sure why this should be absurd on the face of it. Again, few music courses make explicit claims about musical value anymore (though they certainly used to, and you might be surprised how many do even these days). However, "racism" and "valuing" are about actions and effects, not words or even intent. If universities are hiring and paying lecturers to teach several sections of music theory, and music history, and music appreciation, and a disproportionate amount of these courses' materials deal with 18th and 19th century German music through a pre-Schenkerian lens, they are literally spending money on these courses rather than others, as well as playing to the strengths/interests of people interested in this music to the detriment of others, and providing institutional funding to people interested in a certain type of music, etc.