“Isaiah has no Zoroastrian influence. It was written well before Zoroastrianism had any influence on the middle east.”
You are dead wrong.
https://dailymassmeditation.wordpress.com/zoroaster-and-the-birth-of-an-apocalyptic-faith/
Notice the date here given for zoroastrianism. This was indeed apocalyptic.
Nope.
Zoroastrianism arose in Eastern iran, in what is now Tajikistan. It had no influence in the west of Fars before the 6th century.
The book of Isaiah dates to the 8th century.
Tge tone and text of the Gathas are utterly different from Isaiah.
What’s your argument?