Making Ages era score target linked to the number of cities would even tall vs wide somewhat.
The threshold is based on the number of cities; but, most of the ways you can earn era points- building districts, buildings, sending trade routes- all scale with the number of cities you have. A larger empire has more options to "do things" which is how you get points. It may make more sense to borrow from something like the steampunk scenario that shipped with Civ 5 G+K and do something like, say, reduce the spammable things you can do for points and introduce some other metrics based on you vs other players, like "most gold earned" "most great people recruited" "most eurekas achieved" etc, with those points awarded at the end of the era. And of course they need to scale the thresholds to game speed and map size.
Basically, there should be some effort/investment required to hold a large empire together, and real consequences for overextending. Perhaps there could be some form of "support cost", which would be calculated from things like:
In my ideal vision for balancing, the trade off would basically be:
Empires of similar overall population will, ceteris paribus, be roughly similar in outputs and therefore strength.
Case: 10 cities of 10 pop vs 5 cities of 20 pop -
Wide seeks to leverage the extra territory it has and thus, extract things from terrain (more builders and improvements) and resources (more coal for power, more horses, etc.)
Tall seeks to leverage its citizens' productivity, and thus, likes to focus on infrastructure granting % boosts or yield generated by concentration of infrastructure, or specialists.
The strategic play would be recognizing the best way to leverage what you have available to you.
What would not be a valid comparison is to compare empires by number of cities directly. However, obviously 6's current district balance just skews towards having as many copies of districts as possible which more cities gives you.
If more population (spread over some number of cities) means more overall power, you need to pay for pop- currently we have amenities and housing. I've previously mentioned some ways to make amenities much more valuable, but my real point is that a civ6 player should be allowed by the game rules to have as big and developed and sprawling an empire as he wants-
provided he can support it. If a player manages to have twice the cities and population as another, and he can keep them happy, fed, protected from rivals and rebels, then he deserves his prize. That may mean making loyalty counteracted by generic disloyalty that can create free cities etc, but the entire system really needs one thing to be balanced:
-Expansion vs development needs to be reasonably balanced
for most of the game when good land is available to settle
Right now war is the optimal plan for all victories because it's the cheapest way to expand. Ignoring that nuance, expansion itself is extremely strong. You gain a lot by having
more campuses and zero by having an existing campus and then
improving the campus because, well, you can't really.
Imagine for a moment you are playing civ6: oversimplified edition, where there is just one district which always gives +X yield, and has only one building which also gives +X yield. You have a district in city A. Do you build a settler and settle city B, thus letting you get another district, going from X to 2X, or do you put that production into the building and double your output from X to 2X? Naturally this depends on the availability of land and how expensive settlers are vs buildings.
Now let's change things up. We add in specialists, so a Building can slot the specialist which gives +2X more yield. Imagine your empire can only support 2 population. Now things become a question of population distribution: You have a district w/ building in city A. Do you build a settler and settle city B, letting you build another district, or do you slot the specialist in city A? Well, this is a little more complex because we already have the infrastructure in city A, but settling a new city might allow us to also do other things in the long run.
That's what I refer to when i say development; there needs to be sufficient options to either expand into new areas or improve what you already have. The constraint is that you can only support so much population at once, so if you are able to both expand and develop, you can't do everything everywhere all the time. In order to do more you have to pay the "tax" which is having enough luxuries, ECs, loyalty buildings, neighborhoods, what have you. In the early game there aren't as many options to develop so you want to expand. In the mid game there are options to do both. In the late game you have more options to develop than expand. During the mid game, which i think is the critical period of most 4x games, these options should roughly be balanced with each other, but not perfectly.
We can create positive development opportunities for players instead of just focusing on negative burdens to suppress the growth of expansion. That goes outside the scope of this thread. But, we still need to counteract the fact that more cities grows faster in raw pop than fewer cities, and it's cheap to get "enough" housing and food etc. That's where that whole "tax" and penalties for expansion come in to play (which is ultimately aimed at curbing raw population growth here, but for other posters it can mean the ability to generate yields from districts- which themselves are tied to having the 3 pop to support them.)
