Hey hey, that's no problem. Just wanted you to know a little about who you were talking to before you started jumping to conclusions about how much I've thought about this and what my understanding of the material might be.
The interpretation that Jesus' death rewrites the saving covenant is just that - an interpretation, curated, reinforced, and maintained by religious scholars and followers. There are many other opposing interpretations of that event, and each lays claim to "moral supremacy" (though I agree with KB, that is a detestable phrase). The Evangelical sect makes no argument for moral supremacy that these others do not. Historically, Protestantism is a centuries-long tradition of interpreting religious texts according to changing human preferences.
In fact, it sounds like you explain a familiar thought process. An old paradigm exists that conflicts with a set of mores. The OT "old" paradigm is distasteful for whatever reason - killing children being one of them, ostensibly and agreeably. So a part of the set of known mores is that we don't really want to murder our children for insolently drinking late at night and eating Burger King too often, and so a new interpretation is required to fit our stated cultural preference. A new interpretation is required to fit modernity, how humans now live.
"But PTR, if the text remains the same, how does the new interpretation come about?"
Someone just says it, 95 theses-style.
The Bible is clear, succinct, and to the point: kill insolent sons, deny women public voice, give away all possessions.
Human-interpreted theology is a convoluted maze of analysis, clarification, explanation, caveats, perception, perspective, and omission. "I'll take Cherry-picking for $500, Alex!"
Usher NT "new" paradigms - a la Jesus' Covenant of Salvation - which will soon be OT "old" paradigms in a few thousand years (i.e. now), and the OT "old, old" paradigms are detestably, can't-cop-to-it archaic.
NT "new" says you don't have to kill your children, "Praise God!" It says women are subservient, "Praise God!" It says give away everything you own, "Hell no!"
(note: would rather not get bogged down in passages, as that's a rabbit trail of several hundred pages and 66 books of "wisdom tradition, [...] poetry, myth, history, and correspondences")
And as people realize that they do want women's suffrage, and as people realize that they don't want to give away eeeeeverything, still yet even more interpretations occur. The ancients weren't prepared for modern philosophy, and so now the interpretation of God's omnipotence must also jive with free will. We have to figure out how God's omniscience and soul-saving grace can account for the lost indigenous souls, for babies, for dogs. People choose individually how these fit their morality - they interpret, you interpret, I interpret.
I morally interpret without all that because as long as I'm ethically "winging it", I'm starting from scratch. Explaining and justifying all this 4000 year old theology is not how I want to spend my "long life journey ahead". If it makes you better to choose from an old book, that's ok. I've read some of those too.
But you've got to realize that at the end of the day, everyone's just figuring out what to believe based on what they know and experience. It's a scramble; there's no supremacy to be had.