A small fish to fry

I’ve been doing a lot of extra editorial work during COVID-19. I recently came across this startling opinion of a New Grammarian, who would have us write, “Who’s learning from who.” They (sg.) contend that the interrogative pronoun is always who, uninflected for case, and that it is only the relative pronoun who(m) that is inflected, and even then only optionally. The latter bit is well known, but the first bit arouses tears of anguish: the precept leads to such eyesores as “From who is the message,” and all sorts. Then, I suppose the apocalypse is upon us, so whom cares.