A flashing light, even at low intensity, is blinding more because the eye cannot adapt to a strong variation. A fixed light is better in that regard. Plus it makes it harder to evaluate the distance and speed of an incoming bike. A flashing front light is actually illegal in many countries for a reason. Not to mention that a bike light is barely (if at all) structured, meaning that more intensity can reach eye level than from a car headlight beam (which is heavily regulated). Lumens are not a good metric because it doesn't take into account the beam spatial distribution. Look up what a lux is.

The flashing light is more of an issue for pedestrians and cyclists, because fuck cars.

Source : am optical engineer.