Even at that time, the religion of the Jews (which was not yet rabbinic Judaism) did not have a clear established canon of scripture.

Even now the word Torah most often refers only to the first 5 books, but according to the speaker it can refer to rest of the Old Testament, and it can even refer to the entire body of Jewish religious texts (talmud, kaballah, and everything else). So what did Jesus mean when He spoke of the Commandment of God. What did He include and what did He exclude. I believe He excluded a lot. You can believe what you want.

For that matter, what did Job mean when he spoke of the word of God. Job is the oldest book of the Bible and existed even before Moses was born. Certainly he wasn't speaking about the Bible because it didn't exist. I think the "word of God" does not have a precise limited physical definition. I'd say it means whatever God says. And that brings us back to the question of whether God really said everything that the Jewish scribes attribute to Him.

To stretch what Jesus (and Job) said about the commandments of God to say that it applies to every word of Jewish tradition is ridiculous.

And to assume that it refers exactly and only to the Old Testament as included in the Christian Bible is shaky ground too. There is nothing Jesus ever said to precise exactly which "scriptures" he considers to be the revealed Word of God.

The scribes always accused Jesus of wanting to destroy Moses and the Prophets with His teachings. So its clear He wasn't exactly teaching them as doctrine.

Instead, what infuriated the Pharisees is that He used the OT to demonstrate His Christhood.

It does serve for that. But certainly not as a doctrinal guide.

Paul and the early church did not stress learning the OT, and Paul even warned the Christians about studying Jewish fables.