This is also true for Germany, but your ability to see in the dark decreases at some point with increasing brightness, since you don't allow your eyes to get used to the darkness.
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.
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.