I don’t believe the burden would be to prove that the voice actor was impersonating, but that she was misappropriating. Walking down the street sounding like Bette Midler isn’t a problem but covering her song with an approximation of her voice is.
You are dead right that the order of operations recently uncovered precludes misappropriation. But it’s an interesting situation otherwise, hypothetically, to wonder if using SJ’s voice to “cover” her performance as the AI in the movie would be misappropriation.