In this case, if we reference Galatians 1:11-12, we could argue that Paul himself received the Gospel “from no man.” But what people who dislike Paul don’t reference is his entire point, which is that he was called by God, but that he was accepted by the Apostles (Galatians 2:1-10) who extend him the “right hand of fellowship.” So yes, Paul said to have received the Gospel from no man, but he quickly goes on to explain how he is affirmed by the Apostles. Later, in 2 Peter 3:14-16, Peter, who was one of Jesus’ closest disciples, affirms Paul’s writing as scripture. Furthermore, he notes that “his letters contain some things that are hard to understand, which ignorant and unstable people distort.”
What is generally understood of your question is that Paul used different language when explaining the teaching of Jesus, because Jesus is not bodily present with Paul. The language is different, but the message is the same: forgiveness of sins through faith. And so, because Jesus was not bodily present with Paul, Paul has much less to say about Jesus ministry, and much more to say about Jesus’ saving work on the cross.
Paul certainly recognized that the saving work was through Jesus Christ. Though I certainly won’t cite all examples, this one from Romans 3:21-22 comes to mind. “But now a righteousness from God, apart from law, has been made known, to which the Law and the Prophets testify. This righteousness from God comes through faith in Jesus Christ to all who believe. There is no difference” (emphasis added).
So these points aside, let me end with a quick return to my main point, which more aptly covers your question. Paul was not bodily present with Jesus, so he did not share as many stories of Jesus’ life and ministry. Because Luke compiled his Gospel of Jesus while he was on mission with Paul, it’s likely that Paul knew the stories. However, Paul didn’t spend much time with the other Apostles, so he may not have felt the need to spend much time elaborating on Jesus’ life, and more focus on the mission of Christ. There is also a notable lack of stories in the epistles of Peter and of John. Their epistles read much more like Paul’s, than any of the Gospels. However, the central message of Jesus teaching and the central message of Paul’s teaching are the same: that Jesus Christ was crucified for the sins of the world.
To think Paul corrupted Christianity is just wrong.