I played for about 20 hours so far and in most games the latest I got to is like medieval era, so I can't comment on later eras. However, here is my feedback so far.

 Influence and Culture Spread

First issue I have noticed is in the early game other than Pottery Workshop you have zero tools up until you get Rhetoric to Theaters to get more influence. This causes an issue because some civs have buildings/abilities in the early game to get more influence while others have nothing. I literally had games where a Civ was applying a lot of culture pressure on me and I had nothing I could do about it. It feels like a system with very little player interaction (at least in the early game). This brings me to my next point.

Religion

While I really like that they added religion into this game without us having to wait for a DLC much like influence except much worse there is very little player interaction with this system. Other than civics which can help you get more faith (and that is if you get the civics ill get to that) you have no buildings to really get more faith. I feel like there should be a little more flavor to religions. Maybe add some religious buildings, maybe some units and/or buildings that you can unlock for the religion. If not that, just add some more tools to get more faith other than just civics.

Civics

Speaking of civics, I'm going to bring up two points. First the civics system seems to be very inconsistent on your unlocks. Like I checked the wiki for the first two civics and yet when I unlock them it is random. My first multiplayer game with my friends I got Natural Right and Codified Laws right away, but the other players in the game had an issue. One got no civics in 120+ turns and the other unlocked his first civic on turn 100. Clearly this is a bug, but this needs to be fixed.

The second point is I can go games without unlocking civics. Now again I have not played until the late game, but a lot of times civics are just locked for me. Now I know a lot of civics have requirements for them, but maybe those requirements should show up on the UI and they should be consistent.

Huns

I get it that they should be strong, but they are way over the top and very frustrating to play against right now. Like I get it in history they were strong, but sometimes you need to give up historical accuracy for the sake of gameplay and player enjoyment with a civ and against it. I'm sure there are other really strong civs, but this one really stands out. 

Map Generator

I really like that we can control how many continents we can get and even have the option to spawn in a new world, but unless I'm crazy and really unlucky it seems like everyone will meet each other pretty early in the game no matter what I set my settings too. I like the exploration aspect of finding new lands, but it gets a little ruined when I already meet all the other players on another continent in the classical era. Even in new world options sometimes the new world seems super close.

Districts/Infrastructures

I really like the district system in humankind (it something I wish EL had, but maybe in EL2 if that happens) but I see a few issues when comparing cost to districts vs Infrastructures. Like a lot of times I feel it much more cost effective to get the districts over the early game Infrastructure buildings  (of course keeping stability in mind) cause I generally get a lot out of the districts vs what I would have gotten with the infrastructure. Maybe lower the cost from some early game buildings to make them a tad more appealing picks cause right now I rather not spend 200 production on a granary in the early game when I can get more from a properly placed food district.

Also on the topic of Infrastructure please add to the UI what the current yields from building it would provide. I hate having to see how many rivers, mountains, forests, etc my city has. It would be so much better to just have that in the building UI somewhere when you hover over it in the infrastructure tab.

Another thing. A lot of my friends have gotten to the end game and some of them find it boring that it turns into a "district spam" late game. But again since I have not gotten there.

 
Stability 

Stability need to be rebalanced a tad given that late game district spamming is a thing. Also I have not noticed, but it seem to me that having high stability give you nothing? That strange to me considering all of their past games had something from having high approve. So why not in this game with stability. 

Trading 

I really like luxury system humankind, however I do wish trading luxuries is different was different. It's strange when everyone can get a luxuries from me even though I only have one. Like I rather each luxury and strategic resource gave a certain amount and just have the trading system look at again. It's a good system, but I feel it's not perfect. 

That is pretty much it on my end. Now I heard pollution and resources being scarce in the late game is an issue so hopefully that gets fixed. I might wait for a patch to address the pollution issue before I play that far. Overall Humankind is a good game and I think some balance changes, UI improvements, and mechanical changes will make it even better. Looking forward to what is to come!

Relating to your points, I kinda agree with all of em, specially the one about Map generator, I'd like to see way more customization, like, me personally I'd like territories to be as small as possible but still having a huge world, I don't like the province my city is in being so absurdly HUGE, cause right now I'd say they're oversized by far idk if it's even possible to fill every hex by the end of the game.
The issue about the Huns, I think doesn't have any way of being fixed, I'd consider horse archers semi-ranged and should either do really low dmg when used ranged or really low armor when faced against spears, since archers can shoot units behind walls the idea of having Huns sieging your city like that made a really unpleasant experience cause that's what actually stopped them IRL in many places, a freaking stone wall.

I think you're spot on with the districts, It does become a "Spam" late game, and imho during the entire game cause that, population and tech is the easiest way to get era stars and advance to the next era.
I've tried a run getting 6 adjacent cities ASAP, shitting districts like a madman like having 35 pop cap on the medieval era on most of em, I ended up ruining my run cause combining cities is literally the worst thing in the game right now, I thought it would boost stuff in exchange of stability but it actually destroyed my food, pop cap, production and stability, literally 0 reason to do it, the super expansionist AI got ahead of me like they were shitting stars, which is my biggest gripe, the way to progress through the eras is 2000% onesided towards expansionism, cause even if you have 6 freaking metropolis there's no way you're shitting more districts, more pop and for sure technology, and they don't even need that cause they'll get easy stars destroying units and having outposts that they're probably using for nothing but farm stars.

EDIT: Like, my culture and religion were the first and maybe second throughout the entire match, there literally was just 1 empire that didn't have my culture or religion when I was playing with my 6 cities and it literally meant nothing to me, culture wise I wasn't getting the 50 stab hit every now and then cause my culture was different from the one pressuring me but beyond that it's completely a non factor to advance eras and religion, o boi I found that utterly useless.