I’ve never actually read the book, although I have heard some things about it.
There’s a lot of actual halacha which cannot be taught in a classroom, or published as a textbook. Yes, you can be specific about how much hair may or may not peek out from underneath the head covering, but those halachos can probably be taught in twenty minutes.
I’m talking about areas which are impossible to define, involving the overall appearance (and I do not want to get into any kind of detail). Someone could be in violation of actual halacha while not going against any measurable standard.
I disagree with you that this is limited to a problem with a midah. I even disagree with you, to some extent, that driving a fancy car is a bad midah. What they share in common, though, is that they are both a manifestation of a bad midah.