Ireneus,
I am bemused by your characterising the writers of the Johannine Gospel as doing anything "blindly".
The Johannine community had been expelled from the synagogue community over their High Christology, so they were very conscious of their position.
The Jews did not exist in a vacuum and they were not isolated from the external influences, the greatest of which was and remained the Hellenistic. This is exemplified by their need to translate the Scriptures into Greek (the LXX) and is demonstrated by the impact on Paul's thinking.
The earliest "Gospel", which was Mark's, made no mention of Jesus' birth but this was followed by Matthew and then Luke, who started Jesus' life with his natural birth. The Johannine's, however, started earlier and they harked back to the origin of Creation. (One good myth deserves another.)
Regards,
Doug