Finkelstein,
I agree. Satan sees his genesis at the time monotheism became dominant and entrenched. This took place in association with the Babylonian Captivity and Exile (6th century BCE).
Now that they had only one God, the Jews had to wrestle with the problem that "Badness" existed. The technical term is: Theodicy - Since there is a perfect God, how is it possible for Badness to exist? Previously, the Israelites and Judahites recognised the existence of several gods.
That issue was addressed through the creation of a being who is today known as Satan, Devil, and so on. Initially, Satan was the individual employed by God to do his "not so nice things". At his beginning, Satan was not the evil individual that he became much later.
Doug