Dynamo lights and battery lights are different animals and probably shouldn't be compared directly. I have experience with both and they both have their plusses and minuses.
For a couple years I ran a Supernova E3 Triple which they claimed was around 800 lumens. I would have compared it with a 200 - 300 lumen Light & Motion Stella I had just prior to that. It was maybe a bit brighter than the Stella, but not much. Certainly it wasn't 800 lumens. But it was surprisingly adequate for the riding I did, mostly urban and suburban, where in the suburban parts it got pretty dark in places.
The Supernova E3 Triple has no beam pattern at all and to avoid blinding oncoming traffic I had it aimed pretty much about 25-35 feet in front of me, which was a good spot for seeing road debris and potholes. It did not flood the area like a super bright 1000 lumen light will do.
The obvious advantage was that I never worried about charge or duration or anything. It just worked. Always. I used it as a daytime running light when I rode the bike, which was my winter beater bike.
Honestly, I couldn't tell when it was on or off, so I left it on. Drag exists, but is nearly negligible with the Shimano dynamo I used.
I also own several high-end Light & Motion lights, including the Taz 1200 and the Seca 1400. I often supplemented the Supernova with one of these and they would wash out the Supernova, especially on high.
Ultimately, I don't really recommend a dynamo for off road riding, but for most night riding they're super, especially if you have a bike where they can be mounted out of the way in a permanent or semi-permanent location.
The Busch & Müller CYO IQ T Premium puts out 80 lux (They seem to measure dynamo lights differently than battery lights) and I've seen the 60 lux old version in action and it is a totally usable light for much riding. A buddy had one and it was not necessarily a whole light brighter than my Supernova, but the beam was more useful. You can't really tell what that means until you see one in real life. My next one will be the Busch & Müller, and likely not the latest Supernova. The 60 lux B&Ms I have seen probably are the equivalent of about a 400-500 lumen light but projected to a rectangular pattern in front of the bike, not just illuminating everything. They're useful for on-road riding but I'm not sure I'd like one on a dark single track trail.
I'm a dynamo believer but they're not really the same thing as a battery light. Different missions. For real off-road riding I'd use a battery light. For commuting or general dark road riding I wouldn't hesitate to use a good dynamo light.
Dynamo lights don't exist only because they have to exist in Germany. They exist because there is a market all over Europe of real commuters who ride bikes every day, day or night, rain or shine, to go about their daily business. People who don't believe this need to take a trip to Belgium or Germany or the Netherlands or Switzerland or other places.