Christians, a question about Muslims hatred towards the apostle Paul?

I have noticed that when Muslims try to discredit the Bible they often like to slander the apostle Paul. But think about the hypocrisy.....Muhammad came about 600 years later and even thought that one time he was demon possessed, and yet Muslims argue that Paul never saw Jesus. Well, neither did Muhammad. Why in the world would I believe a man who came 600 years later and thought at one time he was demon possessed? If a man named Isaiah came 600 years after Muhammad and taught a different doctrine than what Muhammad taught would any Muslim just accept it? When it comes to Christianity we have multiple eye witnesses who were tortured and killed for spreading the gospel. How can any honest Muslim expect people to believe Muhammad over the first century eye witnesses? The best Muslims can do is call Paul a liar! Just amazing double standards.