I believe this has been mentioned before, but production merchants are broken with "unlimited units" on. When hovering the cursor over the option, a tooltip says that some units are still limited. Why aren't production merchants included in this group of always limited units?
Currently, I'm playing on epic (6000 turns), and early merchants cost 83 production. However, they provide 99 production. This means that if you build/train 6 merchants, queue unlimited merchants, and use those 6 merchants on the city producing merchants, you'll get 7 back (plus extra, if the city's base production is high enough). So, assuming the city's base production is 83 (for simplicity), the process looks like this (number of merchants, arrows represent a change of turn):
1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 8 -> 10 -> 12 -> 15 -> 18 -> 22 -> 27 -> 33 -> 40
So, in 15 turns, we have turned 1 merchant into forty. If we had just produced buildings or other units, we would have, after 15 turns, 15×83 or 1245 production worth of units/buildings. However, 40 merchants provide a total of 3960 production; we have created a surplus of 2715 production in 15 turns! That's almost 200 production per turn, on average; and if we keep going, the ratio of surplus production to initial production only increases.
So, perhaps these units should be exceptional to the "unlimited units" option. Or, we could just drop its production yield to match its production cost.
Currently, I'm playing on epic (6000 turns), and early merchants cost 83 production. However, they provide 99 production. This means that if you build/train 6 merchants, queue unlimited merchants, and use those 6 merchants on the city producing merchants, you'll get 7 back (plus extra, if the city's base production is high enough). So, assuming the city's base production is 83 (for simplicity), the process looks like this (number of merchants, arrows represent a change of turn):
1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 8 -> 10 -> 12 -> 15 -> 18 -> 22 -> 27 -> 33 -> 40
So, in 15 turns, we have turned 1 merchant into forty. If we had just produced buildings or other units, we would have, after 15 turns, 15×83 or 1245 production worth of units/buildings. However, 40 merchants provide a total of 3960 production; we have created a surplus of 2715 production in 15 turns! That's almost 200 production per turn, on average; and if we keep going, the ratio of surplus production to initial production only increases.
So, perhaps these units should be exceptional to the "unlimited units" option. Or, we could just drop its production yield to match its production cost.