I'm going to show my lack of cycling knowledge here, but I really don't understand what you're saying. Why wouldn't one just use the rear break and set their body, like when one rides a bus and has to stand?
The only time my rear wheel has left the ground while braking is when I've tried to do it intentionally. And I've made plenty of hard stops in thousands of miles of riding.
The real limiting factor on road bikes is traction.
Disc brakes on road bikes might give a distinctive advantage, even with greater weight. Disc brake rims need not have a braking surface and thus can be lighter having less angular momentum.