Those are just ridiculous classes, and I hope I'll never see them in GT. In fact, I'm pretty confident I won't. You can't just rank cars by their HP. Two 400HP cars can lap with seconds off of each other, or a race car with 200HP less than a road car can still beat it, and so on. This isn't the way to go.
Besides, if I want to have a challenging race by taking on cars from a higher class, let me have it. I'd throw the game out of the window if it won't let me.