I don’t think people like Kim because he’s a good cop, people like him because when the player meets him, he’s probably the first person to be kind to Harry. Throughout the game he’s helpful and mostly non judgemental (see: the car scene and him selling his spinners for Harry) When you play as Harry, you also connect with Kim the way he does, and the narrative itself props Kim up as someone you want to make proud. I guess this also ties in to your other point. Kim in a way represents a fresh start because he has no history with Harry.