No your screen is not faulty. These are a TFT screen and as such have a fixed luminosity.
This is one hardware item I have never been truly happy with, although I did get used to it.
I found having the keyboard stand arms set so the keyboard tilted downward slightly makes a bit of difference. I also have a couple of wedges I use when using a keyboard stand that only has fixed level arm supports.
My latest is a modified music stand, where I modified the mounting bracket on the rear of the 20" LCD monitor I have, to actually fit onto the music stand. Works really well.
BUT downside is the monitor is too big to use on stage.
I did find the smaller 10" LCD monitors fitted nicely on the Lionstracs Music rest. And they had a nice low profile which meant they were not as "visible" when performing.
And indeed I was going to use one of these live, just before I sold my MS last year in frustration
!!!! LOL, I also sold the small monitor too, darn it!!