I've tried to figure out why smallpox gain so much growth speed compared to largepox.
I think I've come up with two tweaks that wholly or partially might address that growth speed advantage.
1.) Remove the bonus worked tile for every city. This can be done in two ways:
a.) For a city size 1, it ONLY works the tile it is located on. To make it work an tile that can be chosen at the players discretion, the city must be enlarged to size 2 explicitly (using migrant or settlers).
b.) Cities don't get their own tile as bonus. Their own tile is optional to work though.
2.) Make granary size constant. So, the number of food needed to grow from size 19 to 20 is the same as the amount of food needed to grow from 1 to 2.
If cities, by granary growth, are restricted by the game engine to never may grow faster than 1 size per turn no matter how much food they produce (say, they produce twice the granary size per turn in food), then a solution might be to set the granary size large enough (e.g, set it to 50 or 100). This might make it take long time for a size 1 city to grow to size 2, making it viable to use multiple settlers+migrants to create a strong enough start city.
This might not totally address the smallpox growth advantage, but I think it could alleviate it to a large extent.
Your thoughts on this?
(Let me know if a vote on this had been more appropriate)
Yes the two reasons you mentioned are the main reasons why smallpoxing results in faster growth than largepoxing.
However smallpoxing has a major disadvantage as well. The more cities you have the more unhappy the cities become. If you have 50 cities in monarchy, even your size 1 cities go into disorder. Communism does not have that problem but small cities of a communist nation can be easily bribed by democratic nations. Another disadvantage of smallpoxing is it takes much more time to play your turns. That said, I think smallpoxing in communism is still too powerful compared to largepoxing in democracy.
There was some discussion of this a while ago in LT30. It was suggested that instead of the current arbitrary rule to prevent smallpox it would be better to remove the advantages of smallpoxing by making it economically undesirable.
For example - using citymintrade of 3 or 4 so cities wont accumulate any trade before they grow. A player could still build many small cities but they would have no research in the early game.