That's been going on long before Christians even before the agreement on the Bible. A few interpret Genesis as a literal history. Most Christians don't.
But it's not something that will cost anyone his salvation unless he demands that all Christians must believe it as he does.
You remember what Jesus said? When the Son of man comes will he find faith on the earth?
John Calvin, John Wesley, Martin Luther, Melancthon, and John Knox all stood for a young earth and a literal 6 day creation. The Protestant reformers stood on the word of God. It was God's word and God's word alone which they believed and taught.
I have to laugh at your argument against believing Josephus. He was a historian, not a theologian, and he is widely considered to have accurately recorded the history of the Jews. As such I quoted him as he is an authority on ancient Jewish beliefs and history. You can keep on saying he's not believable, but his writings are still published and read because he was known tell the truth. But, that won't matter to you.