I understand the on-going frustration with the game, that up-ends so many things that people thought were 'standard' in Civ. I've been playing since Civ II, including all the Near Civ versions like Test of Time, Revolution, Colonization, and SMAC, and would simply point out that under the 'Civ Umbrella' there has been room for a lot of variation.
As to the history in the game, or 'how history works', I'm a published (military) historian with an advanced degree in history, and I'm not entirely certain I know 'how history works' - there are far too many variables demonstrated by historical events to make such a bold statement.
Fort instance, some civilizations (at least, in game terms) did not last much past a single human lifespan. The American Confederacy (frequently mentioned as an 'Alternative Civ' in the game) lasted less than 5 years. Alexander the Great founded over a dozen cities - the classic definition, by the way, of Civilization - and his Empire outlasted his death by - months. And what followed was a distinctly Hybrid civilization combining Classical Greek and Middle Eastern elements of culture, science, technology, and political structure, which is called Hellenistic to define it from everything Greek or Mesopotamian that came before. For a later example, Hitler's "1000 Year Reich" lasted 13 years. It had a lot of very distinctive elements that separate it from anything previously or subsequently German, but lasting longer than a single human lifespan wasn't one of them.
Which is not to argue that Immortal Leaders was ever my favorite part of the game. On the other hand, having a distinctive human face in front of you makes it very easy to keep track of Civs in the game, and psychologically it is easier for humans to keep track of human faces than any other symbol: no other 'icon' will work quite as well. Given that Civ VII has deviated dramatically from the traditional Political/Military Leaders used before, it is obvious that they are emphasizing the Symbolism of the Leader rather than any historical accuracy: neither Ada Lovelace nor Ibn Battuta, among others, ever had any political leadership or significance historically, but they make fine symbols for whatever Civ they are leading in the game.
Which, again, is not to say that a known political leader of a known and associated Civ wouldn't be better, but, as I have posted before on these Forums, there is NO known human civilization that has lasted 6000 years, despite modern nationalistic fantasies to the contrary. IF something has to change in the game, the Civilization is definitely in the running for the subject of change.
I think the Civ changes could have been better done in the game, but in a game those changes have to combine, at least, Playability and Gamer Agency - that is, the gamer has to have some definite input into what, how and when the changes take place, and how emphatic those changes are. I don't think the gamer has that in the game at the moment, and that and the stiflingly rigid Legacy Paths to individual Age and Game victories mean that (for me, at least) the game is rapidly becoming Boring after only a few months of play.
Without dramatic changes to the game, I'm afraid for me it's Anno 1800 New Horizons Mod or Farthest Frontier, here I come . . .