Peter, rock, build church......
In the Greek the words are not the same, there’s a gender difference giving a slightly different meaning to the root word.
Not to mention that Jesus didn’t say to Peter *On YOU I will build my church*, but rather *upon this rock* which would be a weird way of telling Peter that the church would be built on him.
Yet both are used in Scripture to refer to Peter. Your claim only can only be made if you limit your study to Matthew 16:18. However that argument falls flat when you read John 1:42.