I completely disagree with that very modern and very western perspective. It comes from reading Paul through an Augustinian and Latinized lens. But if you read Paul as the Greek Fathers read him, and if you look at the most ancient writings that name him, as well as Peter and James and John, all as influences on the same men, such as Ignatius of Antioch and Polycarp of Smyrna, you will see that the Apostles, including Paul, all shared a common message. If you read him as Origen read him, or Gregory of Nyssa, with the mystical eastern theology of the Orthodox Church, you will quickly change your mind, and see that Paul was simply faithful to the teaching and mission of Jesus.
Also, and for example, we learn from a careful and scholarly reading of I Corinthians chapter seven, that Paul adhered to a basic knowledge of a Quelle that circulated so widely that those reading and hearing his letter knew the teachings of Jesus from a source other than Paul.
In the book of Acts eight complete chapters go by before the conversion of Saint Paul. What we learn from chapter 8, is that an entire system of evangelism and entrance into the fellowship of the church had already been established before Paul became part of the church. Philip preached Christ to the Samaritans in the eighth chapter. The obvious meaning is that the message was already something that was uniform among all of those who preached the gospel. Furthermore, we see that initiation into the Church required baptism, and the sacrament we call Confirmation, that is the apostles Peter and John coming from Jerusalem to lay hands on the Samaritan converts so that they would receive the Holy Spirit. In speaking with the Ethiopian in the second part of that chapter, Philip used the Suffering Servant passage, Isaiah chapter 53, to present the Gospel in terms of Christ, dying as the atonement for our sins, and rising again, all of which has to be what he drew out of that chapter when speaking to the Ethiopian and answering his question.
All of this was firmly established while Paul was still known as Saul, the persecutor of the disciples, that is of the Christians. No, Paul did not “invent”any of it. 
