I think I understand the physics (I’m a physicist), and on a flat, dry road you are right. These are relatively easy conditions. I can catapult myself over the handlebars with one finger on my mountain bike.
My point is that on descents with twists and turns doing “max brakes” is not what you want to do. You need to modulate braking according to the grip you have, and the feedback you get from disc brakes is one factor that better allows you to do that. Think of anti-lock brakes: on a dry road surface in a straight line you don’t need them as much. Add steering or snow and ice, and they are a game changer. It’s modulation and feedback, not braking power that is the difference.
If you don’t agree, can you explain why so many riders feel safer and faster on disc brakes? What do disc brakes allow them to do that is harder to do with rim brakes? (This is not a rhetorical question, because I really want to know why I am wrong in case I am wrong.)