I remember reading somewhere on this sub a while back that with Roman and Greek Paganism, scripture and canon is not so much a concept as it is in the common religions of today, e.g. The Bible is the word of god, and instead it was the traditions and rituals that they held sacred, but otherwise mythological literature was not held to such a standard.
So in the case of Vergil's Aeneid, how did the Roman people (Under Augustus) view the epic poem? Was it just a good piece fiction with a healthy splash of Roman ideals? Was the story of Aeneas after the fall of Troy already well known to the common Roman before its completion? Livy also wrote about this Genesis story in his Ab Urbe Conditum which was ostensibly history to them, wasn't it?
For a genesis story it certainly seems to have its focus on Roman Identity and Rome's supposed ancestry, but at the same time isn't it really a nod off to the Odyssey, which seems somewhat conflicting to the whole Roman Identity theme with its hands in Greek story structure.
I think whether it was "true" or not isn't really the main idea, but rather what it meant to the Romans. You're right, it was about identity. Virgil's story meant to portray the Romans as descendants of an ancient line; to give legitimacy to themselves. Much of ancient Rome was rooted in Greek culture, this served to create a sort of parallel. Think of the context, even at the time where Rome was taking over most of the Mediterranean world, they were still a bunch of upstarts. It was meant to legitimize everything they had done up to that point: the Punic Wars, Carthage, end of the Republic, and Augustus as the head. Yeah, I believe Virgil took quite a few liberties, but the thing with Roman literature and histories is that the ideas presented are the more important aspects.