No Christian believed Jesus was planning a new church? Guess telling peter he was the rock on which he planned to build his church was a mistranslation put in by (place favorite conspiracy theory here... the claim predates Constantine so don’t try that one).
One Billion Catholic Christians and half a billion Orthodox and Eastern Christians believe Jesus founded a church. Taking one quote out of context doesn’t make them wrong.
I know all Catholics don’t reject the OT. “I am the LORD your God. I change not”, Malachi 3:6 From before the foundation of the world, Jesus is. “Behold the Lamb of God, slain from the foundation of the world”. It was God’s plan from the beginning that Jesus would be the atonement. The Jewish sacrificial rites were a foreshadowing of His sacrificial death. You cannot remove the OT from the New. Jesus is there from Genesis to Malachi.