The problem with immortal leaders is they don't feel consistent and make diplomacy strange. Other civs will hold onto grudges from hundreds of years ago so bitterly that it prevents cooperation so the constantly shifting alliances to deal with present day threats cannot exist in Civ because the leaders are still too hung up on something that happened a long time ago.
If you try to imagine Civ as a game night with leaders across history it makes a little more sense. Of course Cleopatra is going to still be mad at me at that city I took at the start of the game she will probably still be mad about it tomorrow when we talk at lunch. But then why does Peter find rampant warmongering more palatable in the classical age than in the industrial? Does he not have a consistent view on the morality of war?
It feels like the game needs to decide if its a board game against historical leaders or more of a simulation of history and try to simulate the many changing alliances and enemies that occurred.
So I'm quite happy to see immortal leaders being left out. It does make me wonder how diplomacy will be conducted now, I imagine they will still want to give a 'face' to each civ perhaps through a diplomat or emissary type character perhaps using that 2.5D visuals they use for Endless Legend and Endless Space 2.
The grudge-holding and inconsistent motivations would happen with AI regardless of if we had one leader or a dozen per civ. I don't see how having a single figurehead has any bearing on this. It's certainly a massive low point in Civ's overall game design that could use a massive overhaul, but I don't see
mechanical issues as relevant to what is largely an
cultural and artistic issue.
The one benefit of immortal leaders and indeed the overall static nature of VI's cultural representation is that all peoples, regardless of era, regardless of technological achievement, are treated as equals and have equal potential for growth.
Every civ, regardless of when it achieved its heights or how high it reached, starts from ground zero and builds itself up. Even the Mapuche. Even the Kongo. Even the Maori. While the window-dressing could stand to be even less westernized, as I observed before many aspects of the design are not
that offensively Euro-centric, and more importantly Civ VI by and large tries not to exclude large and important demographics in its roster simply because they weren't a textbook "empire", and does so without designating any playable civ as "lesser" than the others.
Now, whether or not that scratches your particular itch for a historical game is up to you to decide.
How many Native American peoples is HK representing outside of the western idea of "imperial powers" (i.e. Aztec, Maya, Inca)? How many Sub-Saharan peoples? And would those even be appropriate in a "cultural melting pot" game?
The Civilization franchise has been criticized for
years as being too Western-centric in its approach, both in misrepresenting native cultures of Africa and the Americas, as well as generally omitting them altogether. As far as I can see from what you prioritize in your lineup, Humankind may in fact be
regressive if the most you care to include on top of Aztec/Maya/Inca are the Olmecs, the Pueblo, or the Mississipians, the Sioux or Iroquois, and even of those options I am not optimistic of their chances of being included at all. Nor am I sure of the political propriety of how native tribes would be implemented and received in a game that is
even more insistent on an iterative "edifice" model of civilization than the Civ games are. Can you imagine the pushback of, say, the Cree or the Sioux, being portrayed as an emergence of Assyria or Khmer? It's a bit of a Catch-22.
I understand your Roman/Aztec analogy--I think many of us history nerds find alternative history compelling--but that usually tends to come down to an extremely short list of environmental features: rivers, temperate climates with good farming soil and carbs, domesticable labor animals, ports, etc. Things which VI already covers and gives universal opportunity to every civ, making VI already quite effective at illustrating "what if" a non-dominant culture had developed during different circumstances (or vice versa, loosely, if you settled in area without key advantages). So while the "mashup" idea is superficially intriguing, I don't think it actually encourages any meaningful speculation as to why any of these civs developed differently. Not when the "controlling factor" for such differences isn't environmental, or technological, or societal, but simply because the player clicked a level up button irrespective of any particular board state conditions.
I suppose HK seems fun if you prioritize playing god over historical plausibility or enjoy the very indulgent idea of cultural fusion. But historical fantasy that far removed from reality doesn't scratch my itch; expatriated wonders and religions are about as much as I can tolerate and even still the Great Persons in VI don't sit well with me. I'm sure all of you are working very hard on this and I don't like belittling artists, particularly since HK seems like a massive--imo, too ambitious--undertaking that you all have investing quite a lot in. I appreciate that you guys had new ideas and are trying to make them work, even if from my perspective it seems they were massively diluted and convoluted in the committee design process (and that, I emphasize, is not really your fault, just how the gaming industry tends to operate absent a strong creative lead and a lot of serendipity). Regardless of whether I personally like the direction this is going, I wish you all the success in just getting the product out and turning a profit.