the problem with your scenario is that zorastrianism
preceded christianity.
not vice versa as you have it.
Zoroastrianism actually wandered 'less far' from God's Word than most other of man's inventions (just what were our Mayan and Aztec cousins thinking of??), and in fact some of the great Persian kings had affinity for the Hebrews and protected them (e.g., Cyrus sending the Hebrews back home, from their Babylonian captivity).
So from an archaeological dating perspective you are correct, Zoroastrianism preceded Christianity by around 500 years, however since Christianity was founded on God's timeless Word (including the historical record from the Creation) - Christianity is built on the unvarnished Truth, whereas Zoroastrianism was an offshoot of this Truth.