OpenAI's mistake was caving to SJ. They should have kept Sky and told SJ to get lost. If SJ sued, they could simply prove another voice actor was used and make the legitimate argument that SJ doesn't have a monopoly on voices similar to hers.
Or... hear me out... maybe they couldn't prove that, which is why they caved. Caved within a day or so of her lawyers asking "So if it's not SJ's voice, whose is it?"