I agree with you. And I agree that the Early Church used it, which is much more important to its legitimacy as a source for its eventual canonization at Trent.
However, I think it's important to acknowledge that the Jews in the Holy Land did not use it, and for them, the canon was only the Torah and the Prophets, but not the Writings (although the Psalms were held in high esteem). This is backed up by the NT, as both Jesus and Paul refer to Moses and the Prophets, but never mention the Writings, except the Psalms.
In fact, given that Jesus accepted only Moses and the Prophets (and held the Psalms in high esteem), I find it odd that the Early Church accepted the Septuagint. But since it is Protestants that don't accept the authority of the Church, that is something for them to wrestle with.
But please remember, the books in question - the deuterocanonical books - were from the period after the conquest of the Middle East by Alexander the Great. Some of these books may not have been translated at all, but were originally written in Koine Greek. Some were probably translated from Aramaic, not Hebrew.
Of course what you say about the Hebrew Scriptures is true, following the tripartite division of the Jewish Scriptures: Torah ("Law"), Nevi'im ("Prophets"), and Kethuvim (*Writings"), with the authority in that order. All of these later texts, whether originally written in Greek, Hebrew or Aramaic, fall into that third category. Moreover, the Jews don't consider the book of Daniel to be among the Nevi'im, but rather, among the Kethuvim.
Does it matter?
A bit, yes.
One cannot come at these things like a Protestant, pretending that there was this solid book or corpus of scrolls that everybody agreed was "the Bible". That is simply not so. To the Jews, there was the Torah - which was THE scroll. The prophets were important, and read out in synagogue too. Once we're down in the Writings, though, they were many and varied, and there wasn't an effort to make a "canon" out of them. Josephus, who was himself a First Century Jewish priest, writes of the 22 recognized holy books. But the Massoretes used a 24-book canon.
None of these things were as fixed as they are today.
Also, even more importantly, the Jews were not Sola Scripturalists, and neither were the Catholics. First Century Judaism was Papal - The High Priest was the Jewish Pope, and even greater than the Pope, for he was a living prophet of God in a prophetic office. The Catholic Papacy has never claimed such things.
Authority in the Judaism of priest and Temple did not flow from the book. It flowed from God down through the High Priest, then the high priesthood, then the Levitical priesthood. As with the Catholics and the Bible, the Torah was not a thing that could be wielded AGAINST the Temple and the priesthood (other than by Jesus, of course, for he spoke with the authority of God). It was, rather, the written record of the past, of which the living priesthood was the heir.
That is certainly not Protestant thinking, and in a Jewish world that has had no priesthood or Temple for nearly 2000 years, the habit of looking to the Book as the ultimate authority is also ingrained. But it was not so in the First Century: the High Priest was the prophetic, living embodiment of God, and the Sanhedrin, the High Priestly Court, was the Supreme Court of the Jews, deciding what the Law MEANT, just as the Supreme Court does today.
It wasn't until the 900s and 1000s that Jews really developed a book-based "Scripture uber alles" tradition in the Protestant vein, and indeed it is suggested that the Massoretes themselves may have been Karaites.
Of course other Jewish traditions reject Karaitism. Maimonedes wrote that the Karaites are heretics.
I think it is a mistake to think of the Bible the way the Protestants do or as Karaites did (and still do). The focus on text above all other authority is not the religious culture of First Century Judaism OR Christianity.
