That Saint Augustine was converted through reading Scripture has no bearing on the fact that he understood it to be the Church that gave authority to Scripture. In fact, it was the Church that decided the Canon, so how can you state that reading Scripture was "outside the Church"? It was the Church itself that decided on the books that went into the New Testament!
The Church does not give authority to scripture. It is God's word that does and that's what Augustine recognized.
" It was the Church itself that decided on the books that went into the New Testament!"
Just as the Apostles recognized God, by what He had to say, so to did the men who read his words since then. The books of the NT are written by apostles and their associates. They were not written by Church members throughout the ages.
The Church has replaced God?
The word preceded the church, not the other way around.