Adapting to the darkness is not a binary thing. You are supposed to see beside the road by light reflected from your beams. Otherwise you would only see animals when they come into your beam, which is generally too late, you want to see them when they are to your side.
When the lights are essentially so bright that I need sunglasses at night, so my eyes don't hurt, the additional brightness definitely makes me see less, not more.
> You are supposed to see beside the road by light reflected from your beams.
I don't think so.
If you are driving at normal speed (100 kmh in most of Europe) on an unlit country road, with a low beam, maybe with oncoming traffic, you have 0 (zero) chance of spotting a deer by the road jumping out from the dark in front of you. Zero. Nada. Null. LED or halogen lights, doesn't matter.
But regardless, I still remember driving with a halogen low-beam, it wasn't any better in that regard than with LED. At least with the LED I can see the road properly now, unlike with the halogen.
When the lights are essentially so bright that I need sunglasses at night, so my eyes don't hurt, the additional brightness definitely makes me see less, not more.