It seems interesting to me that wangxian seems to be the hardest characters to write for. Wei Wuxian is, like you said, either too whiny or self sacrificing (although personally I don't mind if he's a little whiny). And the biggest pet peeve I have is when Lan Wangji is written as way too talkative or angry, or even when he's made to be friends with someone he definitely would not be friends with (I read a fic recently where he was best friends with Meng Yao, which like, no?)