Really? I felt the exact opposite. O-Chul's backstory is one of the few parts of the story that didn't work for me because it felt so cliched.
Not quite Mary Sue, but I can't help but feel that the writing for O-Chul and Miko has been tampered slightly by the readers' caricatured perceptions and memes of the characters. Similar to how Yoda spoke more with his tic in the prequels.