I still don't understand the Katrina hate. They needed an expert on witchcraft to deal with what they dealt with. And Hawley made a good supply guy, isn't he where Ichabod got his crossbow?
The problem most people have isn't with the characters in concept so much as with the actors' lack of chemistry with the leads and/or their relative mediocrity as actors. Although for me, the problem with Katrina this season was largely to do with the writing. In season 1, she'd essentially been a McGuffin -- the goal that motivated Ichabod's quest and occasionally advanced the plot but wasn't really a source of emotional investment for the audience. Once she was out of Purgatory, it was necessary to define a new role for her, and the writers never really did that effectively. She was never as good a character as the Mills sisters because she was a more conventional female character, defined more by men's desire for her than by her own goals or motivations. By the time they finally gave her a worthwhile and potentially interesting motivation of her own -- bringing back the witch community -- it was too late.
And Hawley never seemed to serve much of a purpose. He was a source of supernatural artifacts and had a shady past, but Jenny already filled that role. He was initially a skeptic, but that was dealt with very quickly, and they had Captain Reyes to fill that role. And he was intended as a love interest for Abbie, but there was no chemistry between the actors, and even the producers abandoned that attempt. But he kept dominating the stories at the expense of Jenny and Captain Irving, two much more successful and well-liked characters who were largely marginalized for the first half-season. Frankly, it felt from the start that Hawley was the result of some network suit's note to increase the white presence in the show. Maybe it wasn't, but that's what it felt like. As if there weren't already enough reasons that the fans were alienated by Hawley.