There is No historical accuracy at all in Civ VI. Apart from from The Civs/Leaders Names and some of their Abilities/Uniques, the Game is just a History inspired Game. A random Religion Systeme, Leaders staying as Civ Rulers the whole game, Tech/Civic Research that is the same for all Civs,...etc and not to mention the biggest nonesense of all (if we look at it as a historical Game): Civs lasting for Millennia!! I mean, Civs in a pefectly historical Game should "Rise and Fall" (I would have loved it if they did the RnF Exp adapted this concept and not the Loyalty flipping as RnF). No Macedon that stays till the Future Era, and No TRs America in the Ancient Era.
And Humankind is no different from this. Yeah, it has a lot of mechanisms that are more realistic and more historically accurate than Civ VI, But in the End It's a 4X Strategy Game, that's based on/inspired by history. And tbh I wouldn't like a Game if it was purely history based.