I can remark that every motorist who's ever commented on my Nova BULL or DiNotte 140 taillight has been praising it because it makes me easy to see, and/or wanting to know where I got it. That includes a Sheriff's deputy who stopped and waved me down so he could find out where to buy one for himself, and a man who stopped at the top of a hill on a dark county highway, turned off his truck, and waited for me so he could tell me how well I showed up, and how he wished every cyclist would use gear like mine.
I find that the "noisier" the background, the
more power is needed to (1) be noticable, and (2) see the road surface to avoid hazards. I like powerful lights off-road too, but this Tuesday I went off-roading with a 140-lumen light and could still see where I was going well enough to ride pretty fast, because it's the only light source around and my vision could adapt to it. On a city arterial like the one shown below, however, that same light won't even make a visible spot on the pavement at 100 feet out. When you're trying to dodge grimy black ice domes frozen to manhole covers at 25mph, despite having a faceful of automotive headlights to see past, it takes a bit of power.
If there were a cyclist with a 2W PB Blaze coming towards you, would you see them in this traffic before turning left across their path?
So I'm just stating the obvious: it's situation-dependent. MUPs are a situation I prefer to arbitrarily avoid, because a walker with no lights at all, navigating by the city's ambient "light canopy" alone, will have his night vision ruined by nearly ANY light source. And it's not like you can be 10-20 meters to one side as you approach eachother, MUPs are dinky. Forget it, I'm taking the street
Really not that much excess "lift" in the beam, it's similar to an auto's low-beam. As
RapidRobert said, the light does come from small apertures and can seem very intense, so partly as a placebo move, I will shut down some of the throw power when facing a car directly on a dark two-lane, so they see that "ok, he dimmed his lights, he's not high-beaming me." This also is their cue to check whether
their high beams are off.