I see the biblical text giving a much simpler explanation than what you are proposing.
Exodus tells us that God first spoke the Ten Commandments from Mount Sinai and later inscribed them on stone tablets (twice). The fourth of those commandments was as follows:
Ex 20:8 ¶ "Remember the sabbath day, to keep it holy.
Ex 20:9 "Six days you shall labor and do all your work,
Ex 20:10 but the seventh day is a sabbath of the LORD your God; in it you shall not do any work, you or your son or your daughter, your male or your female servant or your cattle or your sojourner who stays with you.
Ex 20:11 "For in six days the LORD made the heavens and the earth, the sea and all that is in them, and rested on the seventh day; therefore the LORD blessed the sabbath day and made it holy.
The commandment’s “6+1 structure” - to use your term - was, of course, an allusion to Gen 1-2. This commandment was then reiterated in Ex 31:12-17. In all these cases, “six days” is prominent. The meaning of “six days” is far less debatable - if debatable at all - in the two Exodus passages than it is when viewing Gen1-2 in isolation.
If God tells Israel to work six days and rest on the seventh as an act of imitation, how can we say God didn’t work on six days and rest on the seventh?
I’ve pored over your post for a considerable time and while it offers a different way of imagining how the “6+1 structure” arose, I don’t see where we would find the liberty to choose it over what the text actually says.