Yep, exactly, They rate the lumens right at the bar. So, your light bar that supposedly puts out 20,000 lumens, does, when you look at it or like 1m away. But 500m away, it probably can only do 1500 or less. Compared to an HID driving light that is rated at around 5000lm at 1m, still puts 3 or more out at 500m. And puts more that 1500 lumens at 1000m.
Lumens ratings are a marketing gimmick as you stated. Side by side comparisons prove this all the time.
I think you're confusing lumens with "lux".
Lux is a measure of luminous intensity against a surface or object (and decreases with distance).
Lumens is a measure of total light output emitted.
Offroad light manufacturers do use the lumen ratings of the LED emitters themselves to rate their lights, which fails to take into account losses in the lamp's optics, and is part of what fuels this race for the greatest claimed lumens at a cost of spectral uniformity (for the most part it extends over to LED flashlights as well).
Poor spectral uniformity is reason why LED lights appear so intensely (glaringly) bright up close, while having marginal penetrating power into deep darkness: most of the light energy is concentrated deep within the blue region of the light spectrum (around ~450nm). Our eyes cannot discern distant reflections well in the blue region like they can in the yellow-green region, especially if there is a large amount of blue light present in the foreground. Warm or neutral white LEDs (3500-4000°K CCT) greatly increases the amount of yellow-green light emitted relative to blue light emitted (way more than making up for their slightly lower rated lumens).
This is why I stated in a post earlier... until offroad light manufacturers can learn to cool it down a bit on color temperatures, those worried about glare or the bluish light color should forget LEDs altogether and stick with halogen or HID lights. Halogen lights have exceptionally good spectral uniformity, and is why they are so adept at piercing very deep into darkness.