Not sure. As I said, this whole subject gets murkier and murkier the more you spend time with it.
What, then, of the contrast (acknowledged in the NT) between the Sadducees, who were affiliated with the Temple establishment and regarded only the five Books of Moses as canonical (and thus did not believe in the Resurrection), and the Pharisees, who were more of a lay movement and had a considerably bigger canon (and thus did believe in the Resurrection)?
In my reading, that seems to be a contested idea.
AFAIK, the earliest editions of the LXX was indeed just the Torah, and then other books were added, but by the first century the LXX included the full canon of protocanonical and deuterocanonical books.
That the NT writers knew the texts does not necessarily signify that the texts were packaged in the Septuagint at that time. Nor does it signify that these texts were seen as being on the same level as the Law and Prophets.
The NT bears witness to the presence of the deuterocanonical books in the texts known to the NT writers. For example, Hebrews 11:35 alludes to the seven brothers in 2 Maccabees 7 who accepted torture and martyrdom for the sake of a better resurrection.
Now, you rightly point out that there are books in the current OT/NT that were similarly contested in the way that the Apocrypha was. Sure. And there are books that some supported that never quite made the cut. But the Protestant POV has been to stand with the Hebrews in their definition of the canon of Scripture, and it nevertheless remains unclear how the Deuterocanonicals were received by the Hebrews in the first century, before their gradual lack of respect for the LXX--which was, from what I understand, first and foremost grounded in a dislike for what was seen as its faulty translation of the Hebrew--was confirmed.