A noob question (after 13 hours of playing the game in closed beta). 

At the start of the game, a population eats around 8 food. But farmers of non-agrarian cultures only produce 6 food. With granary, this becomes 8 food. Therefore if I have a city of a billion district with a billion farmers, my net farmers' produced food + granary minus consumption equal zero. Hence the only hope the city will grow is "exploitation" (which I assume is the region around a district or city centre).

So when I play agrarian stacking cultures (Harrapan -> Celts -> Franks -> Haudenosaunee) , it feels ridiculously easy to grow. But when I don't, it feels like growth is really a bad thing since my farmers produce less than they consume themselves.

Am I missing something here? It seems like if I'm playing agrarian, I grow like crazy, if I don't then it is a struggle to not stagnate. It feels like a compound interest meme where if you're 1% above 1, then you compound to infinity if you're 1% below 1, then you compound to zero.

Food Stacking: (farmers only produce 50% of the consumption, the culture, exploitation and building bonuses are what keep the people alive)

PS: In the Wiki, Food consumption = 0.1 x P^2 + 8 x P. So not only each population eats 8 foods, they compound 10% of population squared in consumption. e.g. a city of 50 pop will eat 2500 x10% = 250 extra food just from size penalty, on top of the 50 x8 = 400 food the population eat.