Disagreements don’t sprout from text, they sprout from people. Saying the Christian faith is perfect is far from the truth, but in the end it isn’t the church that matters, it’s your personal faith. Again, being old isn’t a factor to demean something, and saying they “kind of” go together is wrong, as they fit perfectly like a puzzle piece. As you said, this was over 1000 years, and having a relatively similar message is impressive when often times they don’t have access to each others works, let alone when they fit together so well.