Interesting thread. I think it's worth a reminder that Jesus did believe in the OT.
Mat 24:37-39 "and as the days of Noah--so will also be the coming of the Son of Man; for as they were, in the days before the flood, eating, and drinking, marrying, and giving in marriage, until the day Noah entered into the Ark,
and they did not know until the flood came and took all away, so will also be the coming of the Son of Man." (LSV)
Jesus said that, apparently. Across the 4 gospels he quoted the OT 283 times. And if we go to Acts, from 6:1 on, in the trial of Stephen, Stephen pretty much summerises the Pentateuch. They believed the OT to be true.
Re the new covenant. Mat 5:17-120 " Do not suppose that I came to throw down the Law or the Prophets--I did not come to throw down, but to fulfill;
for truly I say to you, until the heaven and the earth may pass away, one iota or one tittle may not pass away from the Law, until all may come to pass. Therefore whoever may loose one of these commandsthe leastand may teach men so, he will be called least in the kingdom of the heavens, but whoever may do and may teach [them], he will be called great in the kingdom of the heavens. For I say to you that if your righteousness may not abound above that of the scribes and Pharisees, you may not enter into the kingdom of the heavens."
This law he said not one iota of would change, is of course Mosaic law. All 613 of them.
As an ex long time Bible studying evangelical, now atheist, I think not believing is a massive advantage for reading the Bible. Because we can read what it says, and not what we want it to say.
According to Jesus, Christians should be following Mosaic law. And if believers prefer not to, but want to follow the changes Paul made ( actual and presumed), then they should maybe really call themselves Paulines. Especially given that Paul never even knew or met Jesus.
Even the NT has God, or something killing people, reference Ananias and Sapphira in acts 5. Written before Paul came along. By the same author as Luke by the way.
Mat 18:6 is another interesting one, repeated in other synoptics, where Jesus advocates for a death sentence.