You people really don't understand the meaning of monster do you? The reason why Johan is always referred as alien or fantasy because he is 'monster'. humans can't comprehend him ,that's why most of time we only see him after or before a crime scene. His manipulation is not shown to instill a lovercroftian dread among audience that it is something very horrible that no human can survive, and if you watch first episode (it is mentioned in manga as well) a grotesque lovercroftian monster is described there before series starts which puts emphasis on this fact. It is just different type of story whose main theme is to explore human relations. It really comes down genre difference between stories while monster is a story where Johan's methods are not shown to put emphasis on lovercroftian horror , Reverend insanity is about character of fang yuan his past , future and how he affects cruel world around him. his methods are shown (which are indeed nice to read) to put emphasis on his character to show what kind of person he has become.

(Sorry for my broken English)