How bad does he have to be before he's noticably bad?
Seriously. There's some kind of Dalglish-esque cult warp thing going on with Evans on here.
If he plays quite well, he's the best defender in history. If he plays ok but makes some mistakes, he played really well and the mistakes were someone elses fault (or I just made them up in my head). If he plays badly, it's because the entire defence played badly.
A lot of his performances this season have been in the middle bracket, against sides not good enough to capitalise on his errors. He's played well in some games too, but not often or nearly well enough to overlook him falling to pieces when we have other, less risky options available.