18 And I say also unto thee, That thou art Peter,( Cephas ) and upon this rock I will build my church; and the gates of hell shall not prevail against it. Jesus did not appoint Simon to lead the apostles, he just knew that he would after he received the holy spirit.
Peter fades out after his role at Pentecost, opening the Gospel to Gentiles. It is difficult to make a case that he was the leader.