> The point is that there wasn't a single canon, different sects of Jews had different canons.
You're attaching a lot of weight to a lot of different historical viewpoints. Of course you can find different sects of Jews with different canons. You can find different sects of Jews doing a lot of strange things including committing mass suicide.
However, the majority of the most recognized scholars and historians of the first few centuries C.E. do not consider the so-called apocryphal books as part of the Bible canon. Josephus, Jerome, Councils at Laodicea and Chalcedon, as well as numerous church Fathers (e.g. Justin Martyr, Melito, Origen, Hilary, Epiphanius, Gregory Nazianzus, Rufinus of Aquileia) testify to the closing of the canon outside of the apocryphal books.
> We know that many Greek-speaking early Christians accepted some of the pre-Christian Greek "apocryphal"/"deuterocanonical" works as canonical. Why did they do that?
It doesn't matter. A lot of your arguments hinge on finding obscure debates and controversies. So what if there was controversy among some? The general consensus, however, disagrees with those debates and controversies and finds them irrelevant.
> The canon did change. In the middle of the second century CE, the Pharisees still had multiple canons
You mean the same Pharisees about whom the the Jew, Jesus Christ, said: "Thus you nullify the word of God for the sake of your tradition." (Matthew 15:6)
> And, if we consider other Jewish groups such as the Sadducees or the Qumran community, we find even more Jewish canons than that.
Again, do you mean the Sadducees whom Jesus and many first century Jews condemned? It's irrelevant to even consider any canon that contradicts the most well respected historians and scholars of those time periods. You refer to them as "canons" but they are no such thing. The Hebrew canon was well established by the time of Josephus and only a few obscure sources contradict that.
> And why do you dismiss it as 'some so-called "debate"'? It was a real debate, you can read the Mishnah for yourself
I dismiss it because it's irrevelant. In fact, it's about as relevant as you and I having this debate right now, because neither you or I can change the fact that the canon was well established before the 1st century CE.
> All the Holy Scriptures defile the hands.
You want me to take seriously a document that says that?
> Furthermore, this passage gives evidence that the same debate was active in the 1st century CE as well (and possibly even the 1st century BCE too), through Rabbi Shimon's reference to Bet Shammai and Bet Hillel.
Yes, it was very active -- among people who had no say in the matter and whose opinions didn't mean a whole lot until we decided to throw 20th century criticism into the mix.