But this is the real world. Harry Potter is fiction. And in fiction, if you want something to appear relevant to a story, you have to emphasize it. You can't just say "this character was abused" and then show no scars of that and expect it to have real bearing on the story. A character like Snape does a much better of showing how trauma and abuse shapes a person than Harry does because, even though everyone reacts differently to trauma, Snape has a personality type that people generally associate with someone who went through what he did. He's bitter, mean, and generally angsting and angry at the world. Harry comes off as a completely well-adjusted kid who has really no negative baggage from his life at the Dursley's except that he has to play catch-up with the wizarding world. He doesn't LOOK like an abused kid, even if we're told he is one. And in fiction, you can't just tell about something just because it's a story. You have to show it and bring it to life.