But how can Catholics say this when the official teaching of the church as based on the catechism, and the plain reading of the Biblical text, says Christ will build His church upon Peter’s confession?
Like all reformation Christians, you are trying to build a comprehensive legal case from document not suited to such application. That exercise requires certain inferences that while useful to the “prosecution,” are not comprehensively demonstrable from the source documentation.
Case in point: 2 Tim 3:16 tells us a man of God can not be complete without Scriptures. It does NOT tell us the man of God is complete BY Scriptures.
A somewhat subtle point, but it is the crux of the argument between Reformed and Catholics over the authority of Scripture.
In effect, the dilemma you pose gets no traction with Catholics because it assumes a reformation orientation regarding the authority of Church documents.
A rough explanation, I know. And probably not without faults.
Perhaps the analogy of a “King James Cultist” would work better.
Said cultists have elevated their preference for a particular translation of the Bible to such an extent they perceive a Satanic plot in all other translations. So much so, discrepancies between the King James and all other translations are regarded as prima facie evidence of said plot. (I have even witnessed serious men trying to make the case the Sanhedrin were so incensed by the testimony of Stephen they physically assaulted him by biting)
You see Scripture as a contract, and use inference from other Scripture to fill in the “legal” holes. Catholics see Scripture as a “Constitution” with holes filled in by adjudication by the Church.
Thus, to a Catholic, there is no inherent contradiction between the irrefutably plain statement of our Lord about Peter in Matthew 16:18, and a more metaphoric understanding in the Catechism.