I didn't have the concept of underclass when I wrote the OP, which I think is a large part of why I couldn't get a Firefly analysis to work, since calling Kaylee working-class seems correct in some respects and ludicrous in others. I think what I was initially trying to do was something equivalent of putting the Serenity crew as well as vampires in an underclass, and the Wizarding world in a sort of overclass. And then the idea that Faith and the Winchesters are all underclass adds to the idea that fandom is interested in writing underclass characters (when we're defining the underclass as characters who achieve a significant amount of autonomy from that fact) but not so much working-class characters.

I think seeing these under-/over-classes as both inside and outside the class system can have interesting uses? That is, neither approach is wholly right or wholly wrong? There is certainly something that Faith, the Winchester, vampires, and the Serenity crew don't take part in and as a result derive an increased degree of autonomy as opposed to working-class figures.

Although class cultures, which is really what I was interested in, do seem to carry over to the underclass; Simon doesn't stop acting privileged when he becomes an outlaw, and Faith and the Winchesters remain coded working-class in interesting and important ways.