Late for the battle, but here's my opinion anyway.
I think a lot of people might mistake PC to inclusiveness. Both can be linked, of course, but while PC often has a bad reputation attached to it, less people consider being inclusive as something inherently bad.
And it's the core of the problems: words we use, definition we put on them, narrative that we deduce then... PC versus inclusiveness; historical "accuracy" against historical "accuracy".
Firaxis tried to be more inclusive, gender-related and race/culture/ethnicity related. Less male leaders, less european empires.
Of course, this will appear as a bad thing for people that grew up in an eurocentric culture. Only a fraction of white people controlled the world or have been prominent, and yet for those eurocentric people they "deserve" to be overrepresented. Because historical accuracy is more important than inclusiveness, but they don't realize that their historical "accuracy" is completely inaccurate and biased.
Has CdM be a less impactful leader on the History of France than Napoléon, Louis XIV or Charles de Gaulle? Maybe, but if we speak about impacts, Louis XI (completely modernizing the country from top to bottom), François I (making the country what it is today), Colbert (the one that truly created modern France, more than Louis XIV or any king) Clovis (the founder of the country according to the historical novel) should be considered. So why do we always return to the same three names? Because people are utter liars. They don't want "worthy" leaders, "legitimate" leaders, they just want what they know. But I'll teach you something:
The popularity of a leader is not at all a proof of his impact, his "worthiness" or anything that would make him better than a lesser known leader
And that's why I love Civ 6. Because, while we always speak about Charlemagne, Louis XIV or Napoléon, I had little knowledge about CdM. And, at the beginning, I hated her. But then I learnt to appreciate her, and I learnt about her, and I discovered that she was, indeed, a legitimate leader for France amongst the hundreds France could pick out.
It's as if inclusiveness forced people to learn more about History, and people hate it, because it destroy their fragile view of the world and challenge their knowledge.
And it works for everything: female leaders, non-european cultures, everything is worthy of learning, and Civ 6 is a tremendous medium for it. I learnt more about the Kongoleses (which, before, for me, were just the private gardens of Belgians), some of the History of New Zealand... all of that was good. I see absolutely nothing bad in the choices of leaders and civs. The main complains I have are that some abilities are terrible, but that's game design, not the lore around it.
Also, have you noticed that people that say that Political Correctness is made only to cater for some snowflakes minorities that whine for anything, and yet when the narrative deviates as little from what they're used to, they whines like the snowflakes they criticized before?
As for Slavery, indeed it's an interesting topic... Except that slavery, under one form or another, always existed (and some people would say that even our modern countries aren't free from some sorts of "light" slavery). In an incredibly large amount of cultures, nations, empires, throughout the ages, there pretty much always has been a caste, a subset of the population, that was deemed "not-like-us" or used for cheap labour: actual slaves, of course, but also untouchables, serfdom... My point is that "slavery", under many forms and through various levels of intensity, always existed... Therefore, why having to "explicit" it? If you want "slavery" so bad, just consider that, as an immortal leader controlling every move of your workers, you just have slaves. It's just a level of abstraction. I mean, a fish doesn't has a word for water, so why name a thing that could have no incidence on the gameplay because it would be omnipresent? Maybe just add a Industrial/Modern Era civic, "Emancipation", where the need for amenities and housing increases for your population, to represent your slaves freeing themselves.
Wanting to have explicitly slavery in this kind of game would not be good nor bad for me, but just completely unecessary and superfluous and, clearly, not worthy to be the main point of discussion.
As I said : why always those three names?
Charlemagne is not "French" enough to be considered a leader for France. His capital isn't even in actual France now. He was as much a leader for Germany than France (except that the dynasty seems more French), so either he's a dual leader, or we don't take him.
Napoléon, please, stop with the worship of this bloodthirsty ego atop of some mathematical theorems.
As for Louis XIV, yeah, it might works, even if I'd say that he's not necessarily the most representative of France...
Also, you keep saying that they're the most impactful, but, as I said, you "forget" to mention Louis XI, François I, Henri IV, Clovis, Colbert, Richelieu... Are you sure you're interested in "impactful" leaders or are you just catering to your own, pretty narrow narrow vision of the History of France where the same names came over and over without any subtelty?
I'd have prefered Richelieu too, but only because he could have had a magnificent cardinal hat and be all in red. And we all know that all inclusiveness is unworthy confronted to the power of MAGNIFICENT HATS!