So you claim that Christ, who is the cornerstone of the church was a cornerstone laid upon the foundation of the rock "Peter"? You are further claiming that Peter is the head of the church and Christ is not the head of the church.
There is no doubt among Catholics that Christ is the head of the Church. We also have no doubt that Christ assigned one to be leader when decisions that affected the entire Church had to be made. We see Christ assigning Peter the keys. When the Master had to be away, the keys (along with authority which the keys symbolized) was given to a steward. When a question arose outside of Jerusalem that affected the whole Church, Acts records that everyone met with Peter in Jerusalem. After the Temple was destroyed and Peter was killed in Rome, questions/decisions that affected the whole Church were taken to and decided in Rome.
Why Peter. The Gospels record Jesus saying that if a builder wanted a building to stand, he did not build on sand, he built on rock. What was the rock Jesus was seeking to build upon? We see the answer in the story: Jesus was looking for someone who was given a revelation by the Father--and then had courage enough to speak out. Jesus told Peter that no mere man had told Peter Jesus was the Messiah; it had been revealed to Peter by God. Peter believed and had faith in this revelation of God. We hear Jesus telling the Apostles revelation, belief, and faith in God's Word was the rock on which a Church can be built.
Jesus and Peter also pointed to Christ as the cornerstone, the stone the builder's rejected. Jesus did not reject Peter, not even when Peter denied him. We also see the metaphor "capstone" applied to Christ. The capstone is the top stone in an arch--not only the focal point of the entrance, but the one stone that holds the entire arch in place. Without the capstone, not only would the entrance not have a focal point, the entire entrance would collapse and no one would gain entrance.
It would be silly for people to argue that Jesus could only be the cornerstone, or the foundation, or the capstone--that it would be impossible for him to be all. These are all used as
metaphors to describe Christ, just as "shepherd" is used as well. Likewise, it is silly for people to argue that Jesus couldn't also use a
metaphor to describe Peter, or that he wouldn't appoint a steward on earth when he could no longer be with us physically. Jesus prayed that his disciples might all remain one as he and his Father are one.
Instead, during the Protestant Reformation, people decided the original structure Christ set up--and the Church had followed for fifteen hundred years--could be improved upon. Instead of Christians of that era taking their questions/grievances to Rome and settling them there, some decided to use Enlightenment type politics and division in Church as well.
Catholics decided that Christ as cornerstone, capstone, foundation, and Peter, with his revelation, belief, and faith that is rock solid--not to mention the keys which were bestowed upon him--was the format Christ instituted. Unity (not divisiveness) was Christ's prayer. Therefore instead of going the way of man-made Enlightenment, Catholics decided it was best, when it came to Church, to trust what Christ instituted. That is working out well for us. How is the Enlightenment philosophy working out for the rest of Christianity?