“Do you say that the Apostles’ preaching had less authority than their writing?”
The Apostles themselves had authority and were the foundation stones of the Church.
Churches can exist with no Scriptures - and do today.
Right you are.
Right you are.
This is most satisfactory. And conclusions follow.
The Muslims say that we Christians (along with the Jews) are "People of the Book," but that's not quite right: we are, rather, people of the Word.
And the Word is, in fact, a lot bigger than the Book. The Word is the full expression of God; ultimately, the Son, the Second Person of the Trinity; the Book, precious as it is, is just one form of expression of the Word.
The Bible does not say "For God so loved the World, He sent a Book." It sways "He sent His only Son."
Which brings us to the consideration that the unwritten teachings of the Apostles, which they learned from Christ and taught first and primarily by oral preaching and example, were just as authoritative as the portions of those same teachings which were ultimately reduced to written text. That is the Church being an embodiment of the Word, and an even fuller one than the Text alone: we are the Body of Christ.