So you’re saying that if the Gospel were inaccurate that it would be authoritative?
It’s authoritative because it’s accurate. Again, as St. Paul says, if the Gospel is a lie than we are doomed and we are in our sins.
Incorrect. Josephus wrote plenty of accurate things about biblical events and people--but none of it is Scripture.
Scripture is authoritative because it was authored by God Himself. The people who put pen to parchment were merely scribes.