The Pioneer Bank - problems with the city growth model
Cities gain a growth bonus depending on the amount of food surplus compared to the current population:
+3: Food produced - current population >= 3x current population
+2: Food produced - current population >= 2x current population
+1: Food produced - current population >= current population
+½: Food produced - current population < current population
Cities require an increasing amount of population to increase in level:
Lv 2: 50 population
Lv 3: 200 population
Lv 4: 400 population
Lv 5: 800 population
For a city to maintain a high growth rate food surplus has to be grown at 2 or 3 times the population growth rate. However, this is not possible as food improvements increase at a much lower rate:
Base: 25
Garden: +15
Granary: +35
Storehouse: +40 (seems like a bug to me - should probably be 60 for the improvement is be worthwhile to build)
Skath Pit (Empires only): +60 (if storehouse is fixed then this improvement should be increased to 90 or so)
Even high essence cities with Fertile Rains or having a lot of Towns with grocers/bakeries/butchers is not enough to keep growth high between lv 4 and lv 5.
But worst of all it encourages the use of the "Pioneer Bank".
Each pioneer cost 30 population deducted when added to the production queue. Cancelling the training of a pioneer will refund all 30 population. This means you can reduce a city's population by filling its production queue with pioneers allowing you to keep its
growth rate at +3 (reducing population below the required limit for a given level has no adverse effect on the city). When the city's current population + 30x #pioneers in the queue is enough for a new level then you cancel all pioneers in the queue. Next turn when the city has gained a new level you refill the queue with pioneers. It requires a lot of micro-management to maintain all pioneers in the queue since new improvements/units that you actually want to build will have to be moved to the front of the queue past all the banked pioneers.
A suggestion to a simple growth model without these problems:
Base growth: +0.5 x City Level
Bonus growth: +0.5 per 50 food total
A cap of 2x City Level could be added as needed.