I haven’t really used many of the torches, but the diamond torch produces so much glare that it almost defeats the purpose of using it. It makes it more difficult to see half the screen due to the glare.
The brightness level is fine, but lowering the glare would help.
I find myself using gleam lanterns instead, for the same reason 
yep i always carry at least a piece of cool blue raw and stopped taking the light skill. helps if i run into gleam and my inventory is full! 
I use a diamond torch all the time as my primary light source. Is it a graphics setting issue?
I tried to turn mine down and could only reduce it a tiny bit. I didn’t want to make my graphics ugly to reduce the glare when there are other glowing things to use. It is a bit too bright for the area close to player’s face versus the surrounding area. I dunno about you but I don’t shine a flashlight in my face when I’m trying to light something in front of me. That’s how gems torches are to me xD
I had a post-it on the screen over the diamond torch while mining 
Now I just mine with a lantern.