If Genesis 1 is poetry (which it is not), this would not itself bear on its facticity.
For example, the Australian folk song 'Waltzing Matilda' is poetry, but that doesn't mean there were no jumbucks, tucker bags, troopers, or swagmen. Nor does it not mean there was no late 19th century drought. Indeed, in ancient times, poetry was typically the form of conveying stories (including about actual events).
What is inferred by the claim is that Genesis is figurative or symbolic. However, it doesn't use figurative or symbolic language, it uses historical. If it was 'merely' figurative, then it would tell us nothing about the real world, because it uses concrete language it embeds itself in the real world and sure, it is not about the details of creation, but is clear on the 'how' God's word, because this is intimately connected to the why: God creating in love. The other details of Genesis 1 are also essential to its theological significance, but only because they happened in the world which is the setting of its theological significance. It is modern philosophical conceit that pretends to be able to separate the two.