I’m claiming that there was no reason for Augustine not to accept a straightforward reading of Genesis. He belonged to the neo-Platonist Alexandrian school, and tended to allegorize scripture because of his prior committment to Greek philosophy. But that doesn’t change the fact that Augustine believed in recent creation.
How do you make an assumption that YOUR reading is "straightforward" and that his reading is not? You have no grounds to make such an assumption. He made that reading based on--yes--a "straightforward reading" of the translation he had in front of him--the Vetus Itala.
And yes, he did believe in recent creation. But he also believed in simultaneous creation. You say he was right about A but wrong about B. I say how do we know that he wasn't wrong about A and right about B?
I really suggest you read his "On the Literal Interpretation of Genesis." It's long and hard to find, but it's well worth it.