I saw the whole thing as an inferior Fe story, with even a demonic Fi part where he admits that he resented being stuck at home with his family, thought he was way to smart to be wasting his time with that.
In the seventh book, we find out what actually lead to his sister's death. For most of his childhood, he ignored his sister because he was "too busy getting awards and being Mr. Brilliant", according to his ESFP brother. Then, after his last year, he actually stayed home to take care of her. And he did okay, but then Grindewald came and he started ignoring his sister to obsess about world domination with Grindewald. When his brother confronted him about it, they all got in a fight and one of them killed his sister.
And he carries his shame about that for the rest of his life.
I thought it was a verrrry inferior Fe story.