The contact pressure on a road tyre rather high, tyre compounds play a significant role in traction and braking.

The reduced mass of a road wheel at the rim reduces the energy required to slow and stop it compared to heavier wheels and tyres on other bicycles as a wheel functions as a flywheel. The faster speeds one may see on a road bike is what warrants better brakes as the speed at which the rim is moving is higher and e=mc2 holds true here.

The brake wear on a high performance wheel of lesser diameter like a 20 inch is much higher due to the higher relative speed of that smaller diameter wheel spinning much faster at the same speeds.