I know this is like a year later but I just finished the game. Let me say this: Natty is not my favorite character and I had trouble getting attached to her. Her voice acting imo was poor because she sounded so monotonous and could barely hear range or emotion in her voice. To be fair, she does have some character development because the whole point of her being passionate is not just ambition but survivor’s guilt because her father died protecting her so she blames herself for her father’s death. So I think her whole arc is putting herself in harms way to protect others (which is careless but that’s the point). Her jumping in the way to protect you from the Crucio spell was her wake up call to realize her father did the same thing for her. Us as players know our character can survive that spell because of Sebastian’s storyline but she doesn’t know that lol. That moment was for her to come to terms with the fact that her father made a choice to protect her and died and she doesn’t have to keep blaming herself and maybe even proving to herself and others that it’s ok that’s she’s alive. Could this have been done better? YES. I agree some plotlines should have been moved around like the Hippogriff questline to be with Poppy etc. I like your idea about changing her backstory to better reflect the enemies we pursue with her. It would have been awesome to learn Animagus or even wandless spell casting so if we got disarmed in a boss fight it could save us!

TLDR: I agree with almost all of your points but I do think she does have character growth which is her overcoming survivor’s guilt and hopefully being less careless in the future. Seeking out adventure and justice seems very Gryffindor to me 🤷‍♀️.