I find a nice little summary of the nature of 2nd Temple monotheism in Bart Ehrman’s “A Brief Introduction to the New Testament”, (2004) pp 32. Speaking of the Roman empire Ehrman notes:
As we have seen, virtually all of the religions in the empire were polytheistic. Before Christianity, Judaism alone was committed to the notion that there was one and only one true God who was to be worshipped and praised. To be sure, the difference between Jews and pagans on this score should not be blown out of proportion, as if they were absolutely dissimilar. We have already observed that some pagans, chiefly some philosophers and their followers, also believed that there was one chief deity who was ultimately responsible for the world and what happens within it, whether Zeus, Jupiter, or whoever else was thought to occupy the peak of the divine pyramid. The other gods, including the daimonia and the demigods, were of less power and eminence. Jews, too, believed that there were immortal beings, far greater in power than humans, who existed somewhere between them and the true God. In the modern world we might call these beings angels and archangels; for ancient Jews they also included such beings as the “cherubim” and “seraphim”.
The key difference between Jews and persons of other religions, then, was not that Jews denied the existence of a hierarchy of supernatural beings; the difference was that Jews as a rule insisted that only the one Creator God, the supreme deity himself, was to be worshiped.
The reader can decide how this applies to Mormonism. My thoughts will be in the comments below.