The difference is that from the flight deck you are somewhat distant from the source of light, only see the reflected light, & not all of the light is reflected.
The intensity of proportion of reflected light reduces as a function of the cube of the distance ie approx 2 x the distance to the reflecting object.
Marshallers receive the direct rays, at some distance less than most of the reflecting objects seen by the pilot.
As for brightness less than car headlights? Landing lights/taxi lights I've run across ranged from 100W to 150W.
Most cars have approx 2x60 or 80W on high beam, with the occassional vehicle fitted with a couple of extra 100W driving lights.