A lot of choices in game making are mainly artistic freedom which at first people with a Science or Engineering background tend to shy away from "because it's not how things are".

This is a chorus I like to repeat: Entertainment doesn't need to be realistic to be fun, and I wish publishers / marketers / reviewers / players would acknowledge that more often and stop slapping the label "realistic" and the like on things that aren't.

There are sims that are grounded in careful study and attempt to model some part of reality as accurately as possible, but even they need to compromise, both to run on contemporary hardware and to balance it against playability. But they're often complex, by virtue of modeling a complex reality, and not everyone's cup of tea.

But then you have things like Assassin's Creed that regularly and heavily fudge history, not always in a bad way, but convey an impression of past societies that seems accurate, but glosses over things like the Spartan inequality and slavery or Viking brutality, painting a more "noble" and "heroic" picture than they each deserve.

Again, there's nothing wrong with making up interesting stuff, but people should be honest about it (as you are). Pointing out those artistic choices is an opportunity for learning things. Though the scale of an atmosphere is probably less significant than the scale of Viking slave trade, I still find it curious just how thin it actually is.