It might help if you applied some reason, to give your argument form.
You appear to be arguing that the devil doesn't exist, because the concept only exists within Christianity. I'll ignore, for the moment, that that's easily provably untrue, and focus instead on the structure of your argument.
Does the "fact" that a concept appears in only one source disprove the concept? You wanna rethink that? Likewise, Israel, a monotheistic kingdom, was destroyed by a polytheistic empire. Was your argument that polytheism was somehow superior to monotheism, because polytheists are "noble savages," while monotheists are bloodthirsty conquistadors? How simplistic, for such a well-educated, deep thinker.
I assume, by "the Hebrew Bible,'' you're referring to the books of the Christian Bible written in Hebrew? Or, are you referring just to the Torah/Pentateuch(Genesis, Exodus, Leviticus, Numbers, and Deuteronomy)? There are 39(KJV)-46(Vulgate) Hebrew books in the OT of the Christian Bible, in which there are ample references to the devil archetype, from Genesis onward.
By the way, I studied religion in college, as well as independently, so I suppose I'm technically a "religious scholar," and I'm at least as quotable as any of the sources you referenced...if not more-so...definitely more-so.