The Importance of Paul for Christianity

It has long been said among historical scholars that Christianity is not the religion *of* Jesus but the religion *about* him. In this view, Jesus was a Jewish preacher who urged his fellow Jews to repent of their sins and turn back to God by observing what he demanded of them, so they could enter the coming Kingdom. But Christians did not think repentance and obedience could bring salvation at all. It was the death and resurrection of Jesus that mattered. Moreover, it is often said that Paul was the one who transformed Jesus' gospel about the coming Kingdom into a gospel of Jesus' death and resurrection. Is that true? Wouldn't that mean that Paul and Jesus had different religions? And if so, then isn't Paul, rather than Jesus, the Founder of Christianity?