Lumens is the amount of light, lux is the intensity at a particular point in the beam pattern.

The beam pattern is important. I've had lights with lots of lumens, but the beam pattern is a flood beam, and the result is that the area right in front of the bike is disproportionately bright. My eyesight auto-adapts to the bright area. Then it's hard to see at longer distances, to pick out obstacles with enough time to react. More lumens, the problem is simply magnified. Flood beams are great for off-road riding, where the bike may get aimed all over the place and the stuff right in front of you is in fact the main concern.

For road riding, a more "center-weighted" beam works better. Aimed at a wall, it generally looks like a strong spot with a corona, unless you're looking at a shaped beam typical of some dynamo headlights, in which case it would be more trapezoidal. Played out across 100 meters of roadway at an angle, the strong center spot is covering a large area at a distance, so it makes sense for most of the output to go there.

As Einstein says, everything should be made as simple as possible... but not simpler You won't get the complete story by comparing lumens without looking at how they're being distributed onto the road.