The reason to imagine a different solar system is because it turns out that very little of what we know about geology applies to planets built around black holes. Certainly, it works for physics calculations, but that's why I think of two solar systems which are used depending on what's useful, interesting, and compatible with reality. Also, I did some calculations about the atmospheres of Kerbal planets once and I think they were inconsistent with the dense core model (permission to call it hardcore?). I'll have to check, though, so don't take this as an argument for or against yet.