Paul also said he's an apostle of Christ. Could a Christian be blamed for taking an apostle's opinions seriously?
The gospels aren't neutral historical reports, but works of Christian propaganda to inspire confidence in their followers.
The two passages in Josephus have likely been tampered with by Christian copyists.
The Western Christian view is that's God's lofty expectations are irrelevant because of our original sin. We can't possibly live in the saintly, Christlike way by ourselves, so what was the point of Jesus's moral preaching? God and Jesus knew their plan for our salvation: we would merely have to trust in the sacrificial power of Jesus's death to be spiritually united in Christ and reborn as proper children of God.
As a literary matter, though, the urgency of Jesus's ethical teachings is Jesus's presupposition that the end of the world was at hand. Society's expectations were no longer paramount because God was about to break into the world, and his expectations are much more absolute. That was the apocalyptic thrust of Jesus's message in the synoptic gospels. John is more about Gnostic dualism.
You presume I have no understanding of the history of the New Testament. So have a look at my articles linked below.