I will say objectively that Christianity has been in trouble far longer than Zeitgeist and that scholars in the 20th century have been arguing internally concerning the authenticity of Christ for some time.
Subjectively I will say that I am not convinced that the Sun worship theory is the key component in debunking the Christ story though. Every scholar I have talked to, including an archbishop of Russian Orthodox Christianity has also been aware of the continuing struggle to prove the existence of Christ. Archbishop Demetri eventually just looked at me and asked "does it matter?".
Most state that yes there was a man he was based on, who had a great influence in an time already in turmoil and in need of a focus. This person was in the right place at the right time. Most suspect that his story and message was embellished to answer the need of the times as well.
Lastly: Just think about how our views would be different if just ONE bit of
unquestionable evidence were produced. We definitely would not be arguing it. Yet there is also no
unquestionable piece of evidence supporting the conspiracy either.
Here are some links that show some of the struggles that are occurring concerning the life of Jesus.
Jesus Seminar Scholars Say Jesus Did Not Rise
Contemporary Scholarship and the Historical Evidence for the Resurrection of Jesus Christ
Christianity in Crisis - Turning the Truth into Mythology
Timothy Freke - So What, Don't abandon the Christ Message
Jesus Doesn't Look Like Jesus Anymore, Says Scholar
thre is so much more, but this just points out that the crisis is real and didn't originate with Acharya s
there are
many many books out there on this and have been for a while that can easily be found on Amazon
my two cents, peace