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.
Voice impersonation has been a settled matter for decades. It doesn't matter that they used another actress. What matters is that they tried to pass the voice off as SJ's voice several times.