Moreover, at some point Israel apparently opted for an integrated creation narrative, presumably believing that it gave a more adequate account of the state of the world.

I think they opted (and created) the story that best fit their traditions and supported their community values. 

Neither here nor anywhere else in the New Testament, as far as I am aware (I could be wrong), is it maintained that human society generally would be more just if people observed the sabbath.  

Which is more just, a society with laws that enforce a day of rest for workers or a society that has no rules about when work can be forced?  It seems obvious that Jewish culture was built around just distribution of wealth and just treament of workers.  It is all through the law.

I'm suggesting that "by no other god" they don't suggest that none exists, but that none is declared God by Israel. In the accounts of the exodus, it makes it clear that these people thought Pharaoh's magicians could work miracles also and there are other refernces to other gods having actual powers. These people believed in literal gods with literal "otherworldly powers". That goes for YHWH as well. By having God say "besides me there is no God", the writers suggest that God is declaring his superiority.

 Of course we likely disagree becasue I don't see these as God's words. I see them as ancient Israel's declaration about what God was for them. For them, this meant they would not offer allegiance to any other God.