"Here is the absolute bare minimum of what you would expect of a character with an arc and the agency to accomplish it. What does the fact that you have to struggle to think of an example involving women say about the state of their representation in media?"
But that line of thought simply doesn't make sense, because there's tons of movies where you just don't have such situations, neither for female, nor for male characters - as proven by how easily you can reverse the test, switch men and women and then see that tons and tons of good movies also fail the test. The point of women being used as "plot devices" for men just doesn't stand when the reversal of that test also proves that most men are plot devices or support characters for the main character, too, and not as deep characters. That's storytelling 101, you have focal characters and everybody around is there to support those characters.
So the Bechdel Test is based on a completely false assumption of what characters (both, male and female) in movies are about, and therefor fails to make any coherent point whatsoever. Well, it makes one point, and that's basically: "Characters in most movies focus around a main character, and that one is more often than not a man." - and that's a valid observation, and while I personally don't object to that status I can understand why other people would... but that's also an observation that you can draw from... well, observing stuff, instead of using such a silly test.
Then there's also the problem of false positives and not catching a lot of movies that are genuinely portraying women in a way that the people using the test object to, simply because the requirements are so random. You explain it away by "Yeah, it's not meant to be this failproof test.", but I mean, where else would that fly? "This test detects HIV infections in about half the people who are actually infected, and falsely detects HIV infections in about half the people who are not actually infected. This test isn't perfect, but it's right about 50% of the time, so whenever it detects HIV correctly we can point at it and be like: "There. See?! Greater point about society or something!"" If it's perfectly fine for a movie to not pass the Bechdel Test as you say, that also means that you can only draw a valid conclusion if a huge percentage of all movies created failed the Bechdel test, while a huge percentage of all movies passed the reverse Bechdel test. This just isn't the case, as evidenced by how easy it is to go through a few movies and see which tests they pass. Although it does seem to be weighted in favor of the Bechdel test, I'm not contesting that. But again, that leads back to the focus characters being male more often than not. That is not a problem in itself, but people who want to change that should advocate for more female-led movies, not rely on silly tests.
So again... while there is certainly a lot to be said about how movies portrait and stereotype the two sexes, the Bechdel Test should not be taken seriously by either feminists or non-feminists. It's worthless garbage.