> This sort of begs the question: where does classical OOP, the one taught to all undergrad CS majors in programs that use Java or C++, really fit in nowadays?

Hot take: nowhere. I mostly kid. But really I don't know of any domain in which strict inheritance and data hiding beats mixins/composition, interfaces, and dataclasses. It's so much easier to reason about the behavior of an interface in a given role, than an "Object" which spans all kinds of scopes.