You're right; just because we haven't found them yet, doesn't mean they don't exist, but it is surely worrying that, given the other very ancient written textual material we have, and the massive archaeological efforts that have been devoted to the holy land, we don't have much earlier biblical texts. We have Egyptian papyrus with writing from 2400 BC. Why nothing written in Hebrew until more than two millenia later?
That should be 'I would not go so far....'
One other point: by the 4th century BC, the Greeks had founded most of modern mathemetics, philosophy, the basic forms of literature, etc. The Israelites had invented a moral law, and not much else. And much of their law has by now been abandoned by all but the most orthodox Jews - dietary practices, ritual bathing, prohibitions on cloth from mixed sources, etc.. So I think it's reasonable to call them 'rather unsophisticated'.