Non-coursework PhDs: About comprehesives?

where does it come from!

Quote: "...where does the necessary breadth come from?"

First, I would not accept someone without a master degree into a PhD program. A Bachelor is not enough.
Second: The dissertation discusses all known knowledge of your subject in the literature review and then you add something to the scientific knowledge yourself. The results of your research. That is how scientific publications work. You don't need to do coursework with all sorts of exams, you just study hard. If you decide not to brush up on your knowledge, then yoour dissertation is incomplete, your articles will not be accepted and you won't get your degree.

All sorts of vague subjects are the most interesting. Science is about obtaining new knowledge and being innovative, the more obscure the better. It must be science though, obviously. I got my degree in vcitimology, you probably did not know that was a thing.