This is absolutely the most bullshit fucking take I've ever seen.
Quentin Tarantino says in an interview that he has three main characters from three sides of the story- Shosanna, Aldo, and Landa. Their individual introductions take up the first three acts of the story.
Shosanna is a main character! She was always meant to be a main character! This film is her story as much as it is a story about the other two! She is a central point to this film's plot. This film is hers.
Honestly, whoever thinks Shosanna's story is drawn out in a film where a central point is supposed to be vengeance of the oppressed and antifascism, simply needs to stop talking about this film whatsoever. If anything, there was too little of Shosanna's story. She deserved so much more space in this film.