Isaiah is a newer prophet when Israel was conquered by Babylon. The Pentateuch is much much older. The argument of Isaiah is about the development of God of Israel was the great of all the gods to their is no other gods.
> Epic of Gilgamesh
The whole argument is to ask when was the Pentateuch was written. The scholarship for this has had many arguments with people placing it in 700 BCE (Which was just crazy especially if you read Hebrew) many are placing it to the discovery of written language. Prior to written language we had a very strong oral history. Both Gilgamesh and the Pentateuch have evidence pointing to the discovery of a written language. We have ancient Hebrew (What a pain to read) and it does show a strong relation with Egyptian discovery of writing.
Another interesting this is the uniqueness of the Pentateuch to the other writings from ANE (I had to read a ton of them). The academic discipline in these writing is really interesting and to say that one influenced another is pretty much impossible to do, but it has been shown since the 1860s onward that archeology have discovered allot of sites that date way before what people were thinking and we continue to learn more and more.
Where in Pentateuch does it say that only a single god exists?
Alternatively we have:
When Elyon gave the nations their inheritance,
when he separated humanity,
he fixed the boundaries of the peoples according to the number of divine beings,
for Yahweh's portion is his people,
Jacob his allotted heritage.
The Zoroastrian scriptures are written in Avestan, an extremely close relative of Vedic Sanskrit; this dates it to the late Bronze Age, somewhere around 1000 BC, closer to King David than Isaiah. The date 600 BC is Cyrus' period; later Persians appear to have confused the age of Cyrus, when Zoroastrianism entered the world stage, with that of Zoroaster.
On a personal note: speaking as a Catholic and starting from those premises, I don't see any religious reason to worry about Zoroastrianism's influence on Judaism (or whatever it should be called at that time). God works slowly, and Zoroaster was a holy man living in the age of the prophets; there's no reason he couldn't have received an accurate partial revelation, rather like what Moses got. Judging from Biblical evidence, early Judaism (the Ritualistic Ten Commandments, diviners and soothsayers, the enthusiastic old narrative interleaved with the pessimistic new narrative in the Books of Samuel) would be very unsettling if we saw it today; while post-Zoroastrian-contact Judaism, with angels, devils, and a single supreme God, would be something theologically recognizable and familiar.
(Now I'm wondering about the extent to which magic and astrology crossed over into Judaism from Zoroastrianism. Both practices arise naturally from Zoroastrian assumptions, with Ahura Mazda and Angra Mainyu as approximately peers and humanity as Ahura Mazda's ally, but not from later-Jewish ones...)
I remember a line from a Harold Bloom book (don't ask me which one), something along the lines of "The Rabbis say the names of the angels came from Babylon-- I suspect more than the names came from Babylon."
He was intimating that the idea of angels as divine-but-not-deities God's helpers was "imported" into Judaism during the time of exile in Babylon.
Not True! Scholars put Zarathustra 1000 BCE or even as far back as 1700BCE but [0] but Isaiah at around 700 BCE [1]
Also many aspect of Judaism like the story of flood or creation were copied from Epic of Gilgamesh [2] that goes even further back.
[0] https://en.wikipedia.org/wiki/Zoroaster [1] https://en.wikipedia.org/wiki/Isaiah [2] https://en.wikipedia.org/wiki/Epic_of_Gilgamesh