I Invite you to read Matthew 17 or 19 where Jesus is saying that not a "jot or a tiddle" of the old testament law should be changed, that anyone who didn't follow it would be last, and that he came to fulfill the law.
The argument that somehow Jesus and the NT is meant to water down the Old Testament is completely a surrender by Christianity to modern secularism.
Mainly because all Christian apologetics focus on God being eternal and unchanging, well its the same God in the Old Testament giving all those barbaric injunctions to follow that Jesus is supposed to be the son of. So you can take that position if you want, just know that in doing so you completely undermine all your arguments for Gods existence resting on Absolute Morality, the teleological and cosmological arguments would also fail.
In short, what you just said is an argument against the existence of the God you believe in.