What I don’t think a lot of people that subscribe to the left view realize is that they are bordering on Gnostic theology with this line of thinking. God tells us in Micah that He is the same forever. However, with the Gnostic thought, the God of the Old Testament is a mean, vindictive God who is just looking to punish everyone He can. If God gave all these commands and didn’t expect anyone to keep them because they were there to teach us we need a Savior, then all of a sudden no longer wants people to follow them because the Savior came, that is Him changing.
In these prophets passages though, we see He is upset that they weren’t able to keep them. If you read back in the Torah where the commands are given He says how easy they are and that they are not a burden. He never placed these commands as a punishment or something unobtainable. They are how we live and how we love Him.