Firaxis has made the same game 6 times (sort of). The game does not need early access. It needs a design that is based on what the AI can handle. It is in dire need of immersion.
The problem with you guys (and also me, to some extent) is that you push the game too much towards strategy, when the first two Civs were immersion sims where you could recreate the whole Homo Sapiens History !!! with roleplaying AIs. The earlier easier difficulty levels were here for those who discovered the franchise, and they are still there. Because on a first glance, Civ looks like a hairy management game with specific rules to be assimilated, which is the con to have the pro of that immersion.
(So what kind of immersion do you talk about ? If you want strategic immersion, there's multiplayer, although this one is also broken due to so many various problems. (Pace ones to begin with) But it's here for the diehards. (could be improved))
Now, in face of their own understanding of the game mechanics and in face of the end of the game, Victory Conditions, players tried to find more interest by increasing the difficulty, so that they could check to what point of understanding they have come up, first, and second to have a challenge. Once understood some principles like "the best defense is attack", it became easy to beat the highest difficulty level, especially when the AI was more playing a drama, and you were more likely to look for conquering the whole world, which was funny as hell, but maybe overdated now with the apocalyptic-storm that fall in the corner of our faces (and Christianity/Islam revivals ?), I don't know, or maybe it feels more boring now, after many games, hence the

when it comes to do it. Ultimately, there's the amour-propre of "true" gamers that can try to push you up since Civ3. (and myself I must say that most of my bad reviews of some video games are because of that, I feel hurt there

) But... I think the ones complaining about "dumb AI" have seen through their eyes a blattant inconsistency, that might make them feel insulted. "Oh no developers, what did you do ? Just when i started to have fun ! It must be a joke." Again, for those people there is multiplayer. (theoretically, because : simultaneous turns are not for 1UPT : first clicker wins, unlike Civ4 when the first stack to click could crush into the other one especially with terrain features or walls... so 1UPT has been made so that players have more control on their units and dare more to attack, but have in fact less control because first to click/"the one with better connection" wins. And you will not see anything else than simultaneous turns, except with good old friends and a book on the knees)
But all these are just challenges ; what for ? I will tell you : either you [EDIT : this type of "you" isn't personnal, obviously

] died prematurely and didn't feel the true experience of the game, now trying to turtle-snowball more, either you won a game and want it more real because you feel it was easy overall, like "for good now", either you stagnate to a given difficulty level for good stories and experience (at this point your kind of bored, unless you thought about something that could improve your play doing it) BUT, there exists superior ones. You can't help, don't forget you are a "true" kid gamer and you want to measure yourself to the better and even the best. So either you put your fingers out of your hole and think, either you feel frustrated and hopeless, because below that difficulty level you feel it's too easy and have a feel of emptyness, vanity, and beyond you feel overwhelmed by the AI (worst case scenario, see (1)), either you skyrocket into Deity and feel you have passed enough time on that already, you know, you have other things to do, other games to play, time passes goddamit !

But you have had an *amazing* game experience.
'Cause Civ is Civ : an incredible development of a single species but different cultures on Earth, fighting and transforming the whole globe. That's IMHO what should be kept, along with its "wow effect" : do History cease to be interesting because all the possible out-of-date or boredom ? No ! History has never been that much interesting. That's why I believe we could do something with the roots of the game, beginning in History or even what some would still call Prehistory. But it's not even about History (the invention of writing), but civilization. We need to re-approach the sense of that word. What for ? To show the dazzling, what is the funniest in Civ IMHO, of the domination and quarrels of Homo Sapiens. (the "wow effect") Starting from nothing, to launch rockets in the space. We must make feel the player the difference. And my opinion is that it could be achieved by detailling more the game start ; the middle ; and the end will follow. Make it more difficult to achieve ? What do you hear by difficult ? It's not, IMO, to skirmish with an exploitable AI that have insane advantages. (which Civ AI will always be, don't put your hopes up) It's annoying for those who don't read forums or watch YouTube, and it's too easy for those who use the exploits. It has more to see with the way you build your civ. (what Civ6 tried to achieve somehow I guess) Hmmm Okay, I'm advertising my sig here.
Now, from what I'm aware of, there might exist some Civ games with "unbeattable" AIs. Like Civ5 Vox Populi or Civ4 Sid. So why are you playing Civ6 ? It's not even a question of visual comfort anymore... Fashion. Feel in the move. Play to what everyone plays, Youtubers, friends, developers even !, etc. Have something "new", whatever what. Oh, I'm in that mood, too. But I have that excuse that I'm slow, I never beat Civ6 Deity, while I did once with 5. As to 4, it's too ugly. 3 could be good, but I beat it on Deity once and it was a pain (huge stacks...).
Sorry if some(all I guess

) of you feel I try to lecture the whole forum, but I'm just thinking loud.

I always sound like that when I think loud.
And... YES WE CAN !
(1)[rant] Now what the story doesn't tell, it's that in Civ5 and Civ6, you have to ADAPT ingame, no need to think about it out of the game : there is no gameplay, or the gameplay is fully dependent of your crappy starting location (but you can't do much about it can you ?) and the AI inherent weaknesses (if you notice'em... goddamit i don't even know how science works out of campuses, where is the manual ?) [which can be solved to some extent as proven by Vox Populi, which i know little of, maybe you are right and everything in this Civ5 mod is designed for a better AI - in that case, just hire some AI specialist - preferably the guy who made Vox populi - in the development phase, be it early access, open beta or alpha - if it can be done in a mod, it can be done in any step of the development] and psychotic behavior.[/rant]
Old grognards, I know I know...
And there I notice you are aboard since 2001.
You are missing one important option.
Early access? Never.
Open beta? Maybe.
There is a huge difference between both. Given my perception of the recent history of the franchise, I will never put a pre-product dollar into it again. OTOH, an open beta where they can still chose who to let in but give anyone the chance to give valuable feedback without asking for money upfront, could be a game changer for them. Could.
Maybe, I don't know - but I trust you - but there's also in the differences that an early access implies more deeply its subscribers just because they have paid and also because they can enjoy some part of the game without too much hassle - while in beta or alpha it's mostly a painful bug-tracking for the most part, if you can launch the game to begin with. Now there may be more room for core changes as you say but on the AI topic, as I said Vox Populi have been a Civ5 mod so it could be done at any stage of the development, alike things like tile yields.
Anyway, do you think I should add "open beta" and "open alpha" to the question of the poll ? Or maybe as additionnal choices ?