Look at the Night Elf faces and then compare the Nightborne ones. Are you noticing a pattern? One conventionally attractive “youthful” option and then several wrinkly, angry, unattractive faces.
The poor state of the Nightborne’s appearance is complete developer laziness that still needs to be addressed.
I’ve detailed some of the issues with the playable Nightborne here: Nightborne Customization Thread
No, they shouldn’t. The entire storyline of Suramar was about curing the Nightborne’s addiction and reverting the Nightfallen status.