Where is David_Jay when you want him!
He seemed to be very knowledgable about the history of his people, the Jews. According to David_Jay, the Old Testament was put together a little earlier than the Selucid / Ptolemaic era, but for much the same reasons that you suggest. He appeared to represent Jewish understanding of this matter when he claimed that the Old Testament was written during the period of Jewish exile in Babylon, which ended in 539 BC (and as we here all know very well, began in 607 BC!)
Given that it was the Jewish people after all who wrote the Old Testament, their claims should be given merit, I would think!