I think it is difficult to ascretain. On the one hand, Paul has written so many letters, that later comprised much of the New Testament. This has a profund impact on the many Christians who have the sola scriptura attitude.
One the other hand, much of Christianity’s form and format was passed down from tradition. It was close to 300 years before a standard form of the Bible was disseminated. I believe that Peter had an huge impact on early Christianity. Even Paul looked to him for advice.