If we're having a debate about the idea that some commandments were carried over following the coming of Christ and others were not then blanket statements about "the law" are not really relevant to our discussion, now are they? We're talking about what the law is in the first place. I think that you know enough about logical discourse to know that. As I demonstrated, Jesus very clearly breaks with the priests on the rules regarding the Sabbath. He also makes it clear that dietary laws, for example, are no longer relevant. But he never kills anyone to demonstrate the oppressive legalism of the priestly rules regarding murder. So no. The two commandments are not dealt with in the same way. And therefore, there's no reason to think that pronouncements about "the law" are definitive. You may or may not be right but you need to use more specific evidence.
It would be absolutely foolish to assume that somehow an infallible God made a mistake, therefore sent his son to correct his wrongdoing. It is us that are wrong!
Personally, I think the only way that we can read the Bible to make any sense of it whatsoever is to look at it with the knowledge that the Bible may be about
God but that it was written, translated, copied and compiled by
men. Biblical inerantism, in my view, is not a tenable or coherent position for a whole host of reasons (even aside from being an atheist). As such, I think that the notion of progressive revelation, which I touched on earlier is one of the few ways of making sense of the Bible. And on this view, it is perfectly acceptable to say that parts of what was previously reported to have been revealed are wrong because, on this view, later writers are correcting the mistakes of earlier writers. This view allows for mistakes. (And regardless of how you interpret it, there are plenty of mistakes in the Bible.)
Compare Numbers 15:32-36 to John 8:3-18. In one passage the proper punishment for a violation of the law is death. In the next, there is no punishment. What has changed? Not God. God can't deliberate and waffle in the way that humans do. God is all knowing and timeless and therefore it doesn't make any sense to say that God had some sort of change of heart. However, on this view, it does make sense to say that men have been shown to have made a mistake in reporting the nature of God that was revealed to His prophets and God or one of His representatives corrected said mistake.
Why can't the Sabbath be one of those mistakes? Or accepting that it's not a mistake, why can't it be that God did away with the rule of keeping Sabbath in the same way that He did away with the punishments that He prescribed for breaking it?