I do agree with you on all points. I just, uh, sometimes still do it for fun. I like thinking about how a character might develop differently depending on which House he was in, i.e. which aspects of his character were most encouraged, and how they are perceived based on that, and how that influences characters' relationships. There are some HP AUs that I like a lot. But sorting characters in a vacuum, so just because they "clearly belong to X House", is imo silly and impossible.