Jewish apocalypticism arose precisely in the Greek period of Israel's history. Greek theological ideas and Platonism generally entered Judaism during this period. The idea of "souls" to begin with as something other than simple "life-force" isn't present in the oldest Jewish texts. Of course the oldest Jewish texts didn't arise out of a vacuum either. The oldest threads of Israelite religion are derivative of the beliefs of the Canaanites. Judaism itself we might understand the term, with its strict adherence to the law of Moses, doesn't really arise until pretty shortly before the time of Jesus. Prior to then it's more of a culture with certain feast days and an allegiance to the national god or gods.
Johannine Platonism is basically just drawing from Philo, a middle Platonic Jewish writer. The logos was created to give God platonic distance from crude matter and creation, after all.
All Judaism, Christianity and ultimately Mormonism is a mix of all of these influences (not just Greek and Canaanite, but also Persian, Edomite, Babylonian, etc). If you want to identify Greek ideas as apostasy, then you'll need to cut out the pre-existence and afterlife rewards and punishments from your belief system. Or I guess you'll do as you're doing here - pretend the Greek theological ideas in Mormonism aren't Greek, somehow.