How is Yahweh not immoral?

[Ryantology]

it'd be easier to swallow if God was portrayed as a fuck-up who is trying to improve

True. But even in that case, he wolud have a lot to atone for. Multiple accounts of genocide aren't a simple screw up.

No, but how does a God atone?

You could say that his easing of restrictions and (relative to the OT) conciliatory manner would constitute some form of atonement, even if "I'll never be a murderous psycho to you again" is admittedly poor atonement.