Hello, You bring up the Greek words petra/petros argument and I believe it’s important to note to the viewers that Jesus spoke Aramaic, and the word in the Aramaic is Kepha for Peter and Rock. There is no distinction in Aramaic in this verse, like you are suggesting. There is no distinction in this verse that says this word means a small stone and this word means boulder or bedrock foundation. Simply Jesus would have said, you are Kepha and upon this Kepha I will build my church. An interesting note is to look at Matthew 16 in the French. It came from the same Greek translation but a different language and it only has one word for both-Pierre. It reads, you are Pierre and upon this Pierre I will build my church. Also, many non-Catholic Biblical scholars admit that Peter is indeed the rock.