I don't know, I think Bellerin is a much better defender than Debuchy personally. He just doesn't stay back as much because there's no reason for him to do it. He's quick enough to get back in time if he gets caught too far up. Debuchy isn't, and that's why he needs to be more careful. It might create the illusion of him being more defensive, but really, he's just less useful. 🙂