Zoroastrianism and Judaism were very close. It has been postulated that even Judaism received influence from Zoroastrianism, which I don't think might be a far stretch especially in the Babylonian Captivity. At this time, the books of the Old Testament were being compiled, and some believe that some parts might have been added to or modified based on oral tradition within the texts.
Whatever the case is, all worked out in God's favor I suppose. Still doesn't lessen the value of the Old Testament in the Church. Gnosticism tried to turn Christianity into the pluralistic pagan system, and the Church refused, citing the exclusivist beliefs of Christianity, which is Jewish in nature.
Some of the most foundational phrases and hymns in the Church is Jewish in nature. The very idea of a Liturgy is Jewish.
When Marcion tried to blot out the Old Testament, the Church rejected this, and showed the importance of the OT in the Church. People who converted from paganism and became great leaders of the Church also were indebted to the "philosophical richness" of the Old Testament, which lead to ideas that Plato was really a follower of Moses.
The Syriac Church and the Ethiopian Church has a lot more Jewish elements in their respective liturgies than Hellenism. They were on the margins or outside the empire. Thus, only imperial Christianity, not ALL Christianity maintained Hellenism.
Christianity in my opinion is a lot more complex than Hellenistic. Truly, the Jewish nature is fully embedded and remains. A lot of Hellenic culture and philosophy indeed permeated its beliefs simply because of the imperial nature of the Church, but we forget there were also churches not part of the imperial structure.