The law actually specifies a maximum wattage, which back before all the new technology like LEDs and Xenons actually did limit the brightness... But the laws haven't been keeping up with technology for quite a while...

I was referring to trucks and SUVs that are so tall they blind the cars in front of them even if they are pointed appropriately. Their headlights are at the eye level of other drivers in normal cars.

Output level is another matter that also needs attention

Neither of these are, in fact, the only solution.

We could, for example, have heights that identify other cars in the road and selectively dim the area around those cars.

We could have headlights that keep light below a certain level accounting for both the attitude of the car and the oncoming terrain.

Really how it is achieved doesn't matter, the regulation should just say that, within some cone in front of the vehicle, light levels must be limited to below x for the window areas around any other vehicles.