One thing to consider is that if (and this is a big “if”) the extra brightness is gained by a more efficient LED, and the runtimes are really the same the higher output, the brighter light can be run at a lower setting more often, thus extending run times.

I have a Cygolite 850, on my gravel/road bike and I almost never use the high setting, but it is nice to have for riding on a trail with a lot of obstacles or if I am going pretty fast on the road (which I don’t usually do at night).

On my MTB, it is not nearly enough. When I mountain bike in the dark I want a minimum of 1500 on the bars and 800 on my helmet.

I’ll also add to the comment that beam pattern matters a lot, and a wide pattern needs more lumens. I actually like the Cygolite Metro pattern a lot for street riding.