Settler factories are still a good way to go. If you notice, the rate at which you build settlers is dependant on how many food/shields you have coming in, IN TOTAL. And it totally ignores whether those food you have coming in are being eaten or not, so long as you have enough food to cover what you need for eatting.
So, a city founded on flood plains that lacks shields is a good spot to be building settlers (and I think also workers?), since that extra food has the same effect as shields when building settlers.
So, a city founded on flood plains that lacks shields is a good spot to be building settlers (and I think also workers?), since that extra food has the same effect as shields when building settlers.