You wrote: “So all the arguments before were just about freeing the people and not about why they should be freed?”
This is precisely your problem. You are bringing outside, your own notions, projecting them back on to the verses. I am presenting what I find in the verses of Quran and not my own biased interpretation.
You wrote: “As Allah gave Moses revelation before they left Egypt, this did not need to be written down until after the people were free, hence the mount Sinai episode. This makes much more sense than Moses only told pharaoh to let his people go. Was the Quran fully completed on day 1 of the Messenger receiving wahi or over 23 years?”
Again, same problem as above. You are not reading these verses to get the picture what these verses portray, rather you are bringing your own confusion and external ideas to find and confirm in these verses what your ideas are to begin with. This is terrible. You would call this a Quran only approach?
Yes, Quran was not completed in a day. But Quran itself says so, therefore, I take it what it says, not other way around. Rest is irrelevant in this context.