I suspect you will find 800 lumen to be plenty, even for avoiding debris on unlit roads.
For context, I commute in the dark (and often in the rain) along unlit back roads and along our regional trail system which is unlit double track gravel with forest coverage. I often need to avoid fallen branches, rabbits and the odd deer that pops out of the trees at inopportune times. I have found that my 4 year old Nite Rider Pro 700, which is rated at 700 lumen has plenty of light to ride at about 30-35 km/hr in the darkness even when it is raining. Anything less and I would have to ride slower in the forest tracks. Anything more would be overkill unless your night vision is horrible.
Caveats - Raw output isn't everything - Mirrors are also important.
Raw output is only half the story. Where you put the light is also very important. For riding on the road a light with a properly shaped mirror with half the output can let you ride faster than a light with an inappropriate mirror. Most battery powered LED lights (e.g., Nite Rider, Light in Motion, etc) have symmetrical beams that shine light up, down, left and right. It is great in the forest, but bad for other road users as it can blind oncoming traffic and could represent wasted light depending on your needs. I would contend these lights are inappropriate for most road riding and require higher outputs due to the wasteful light spread.
For context I also have a LED dynamo light that is probably around 200 lumen which I use as my primary light. The mirrors produce a sharp cut-off at the horizon similar to a car's low beams. This puts all of the light generated on the road in front of me where it is needed. It actually reaches farther down the road than the Nite Rider (symmetric beam) at a full 700 lumen. As an added bonus it also does not blind oncoming traffic such as other cyclists on these unlit close proximity tracks. Unfortunately, very few battery powered lights have this beam pattern.
Where the shaped light pattern of dynamo light excels, it also fails. In the forest tracks, where I would like to see off the track and into the forest so I can pick up any deer that may be looking to bolt across the path on my approach (this has happened a number of times) a shaped beam is insufficient. Here the Nite Rider trail light excels. At night, in the rain, I find 700 lumen with this beam pattern to be more than enough at full pace. But because of symmetric beam I need to turn it off (or down low) when encountering other cyclists, runners, pedestrians. Here I rely on the dynamo light so as to not blind oncoming traffic.
Something like the 2000 lumen L&M Secas (symmetrical beam I assume) at full tilt will be outrageously bright and could cause many oncoming road users to hate you or even cause many to crashes or bodily injury (as mentioned by Moz)
Conclusion
If you are only riding on unlit roads with a symmetrical beam light (again most battery powered lights) something with what is now a moderate output (i.e., 300-800 lumen) should be sufficient, even at a faster pace (e.g., 30+ km/hr). 2000 lumen will really be overkill and could be inconsiderate to other road users.
If you are only riding on the road you may also want to consider a battery powered light with a shaped beam (e.g., Bushch & Muller. These are cheaper than what you were considering ($60-120, instead of $180-1000) and you can get the same road performance from about half the output. In some ways this light is superior to symmetrical beams lights for road riding as the reach is much better letting you pick up objects earlier. The hotspot is less bright, as the light is more even spread so some misinterpret these lights as being less bright.
If you ride on unlit mixed roads or on forest paths where you might need to see overhead branches or off the path/road a symmetrical beam will be better.
