Corrective Polemics: Yes; Fictive Construct:No
Polemic is defined as,
an aggressive attack on or refutation of the opinions or principles of another
If then, we regard Genesis 1 as a type of polemic, Genesis 1 is only as fictitious propaganda it is exposing and refuting. This means that the idea that Genesis 1-13 is a corrective polemic is not attempting to imply that Genesis 1 is a mere fiction; a contrived construct. Instead it implies that the facts of the other creation accounts are as accurate as Genesis.
The idea being that they all (more or less) record the same events, but simply put a different religious/political "spin" on the agreed upon events. This means that either all creation accounts competing in this arena which are offering competing theological interpretations of the same events are fictitious, or none of them are. They all share an understanding and cosmology - what happened and how it happened are not in dispute. Only who and why. Yahweh, or Atem. Elohim or Marduk.
What is the Authoral Intent of Geneis 1?
In the OP's question, He states that the ramification of this idea is that
Genesis 1 does not constitute a simple straight-forward educational text. so to restate the question, is Genesis 1 intended to be an educational text; was it intended to be a science textbook or newspaper? What evidence to we have to support either position?
The first major indicator is that Genesis 1 takes the format and style of a prologue. Gordon J. Wenham notes in The Word Biblical Commentary Vol. 1: Genesis 1-15 on page 50 some of the interesting structural differences between Genesis 1 and normal narrative and notes
its syntax is distinctively different from narrative prose. Cassuto (1:11 ), Loretz (1975) and Kselman (1978) have all pointed to poetic bicola or tricola in Gen 1
He also notes that it has an abnormal format
The correspondence of the first paragraph, 1:1–2, with 2:1–3 is underlined by the number of Hebrew words in both being multiples of 7. 1:1 consists of 7 words, 1:2 of 14 (7 x 2) words, 2:1–3 of 35 (7 x 5) words. The number seven dominates this opening chapter in a strange way, not only in the number of words in a particular section but in the number of times a specific word or phrase recurs. For example, "God" is mentioned 35 times, "earth" 21 times, "heaven/firmament" 21 times, while the phrases "and it was so" and "God saw that it was good" occur 7 times.
And these are all distinctives of Hebrew poetry. Ultimately, Wenham regards it as an "overture" to the work and believes it to be "high prose". In fact, several scholars have made comparisons in format and content to the prologue of the book of John - this comparison would be impossible were either one not a prologue.
It seems then that it was not the Author's intent for the readers to regard Genesis 1 as a textbook or news report since it does not take the same format and literary style.
2 Creation accounts
Genesis 2-13 however have no such similarities - these take the format of straight narrative. It is not uncommon for prologues to be or include summaries of the work that they introduce. As such, many regard Genesis 1 as a summary of the works on days 1-6 with Genesis 2-3 being the full story of what happened on day 6.
This however presents a problem as there are ordering conflicts.. In Genesis 1, plants and animals are created on earlier days, then mankind is created while in Genesis 2, plants seem to be created at the same time as man, and animals afterwards. Instead, it seems, there are two disparate and conflicting accounts with one targeted at Egyptian creation accounts and the other targeted at Babylonian creation accounts. It should have been quite obvious to the redactor that these two accounts conflicted, yet the redactor seemed untroubled by this. This tends to indicate that the order and whether it occurred in 7 days or not was unimportant. Instead, the theological significance of the creation accounts seem to be what was important to the redactor. As to the original author of Genesis 2-3, it would be impossible to tell if they intended it to be regarded as fully journalistic or not and it is of little relevance now. Clearly by the time of redaction, it was not intended to be regarded this way.
The implication here is that if background information is required to understand The Bible, then there is no sola scriptura. But at the end of the day, there is no straightforward, plain reading of scripture. We will always be subject to and affected by the hermeneutic circle whether we like it or not and this is how we get prima scriptura in the first place. Furthermore, sola scriptura was intended for salvation, not comprehension. Scripture only may be enough to save, but it is not enough to fully comprehend the Bible.
Like it or not, scriptures were written to a specific audience at a time and place. If you do not understand the occupation of Israel and the exile, then the latter half of the old testament will make little sense. Similarly, if you do not understand the Roman empire, the Gospels don't make as much sense.
But ultimately, we have two very good indicators that the first parts of Genesis were not meant to be understood as documentary: The literary structure of Genesis 1 and the conflicts between Genesis 1 and 2-3.