I apologize if it's been asked before, but what's your main justification/incentive for autoproduction of settlers? To slow down AI city sprawl?
The main reason for the autoproduction of settlers is to stop the ICS tactics by human players. The simple calculation, that it is more profitable in the expansion phase of the game, to build always a new settler as quick as possible for a better profit than to construct buildings inside a city, is not working any longer. It also strengthens the AI, which likes to build early GWs and in my eyes is a much better way to implant settlers in the civ series than to connect them to the "normal" production of cities.
In my eyes connecting the "production" of settlers to the direct production in cities, as it is done by Firaxis, is one of the biggest general errors in the complete civ series, triggering a lot of following problems for a civ game. In history in nearly all cases settlers were never directly produced by cities, stopping all other production activities in that city.
https://en.wikipedia.org/wiki/Settler : The reasons for the emigration of settlers vary, but often they include the following factors and incentives: the desire to start a new and better life in a foreign land, personal financial hardship, social, cultural, ethnic, or religious persecution (e.g., the Pilgrims and Mormons), penal deportation (e.g. of convicted criminals from England to Australia), political oppression, and government incentive policies aimed at encouraging foreign settlement.
As a result, not only the ICS tactics by the human player are stopped, but also the tedious concepts of waste and corruption to block the city sprawl can be greatly reduced and in my eyes the game makes much more fun, when it can be concentrated on units and buildings and not to build always again these boring settler after settler as quick as possible. I think there is a reason, why the Civ 3 succession games at CFC since many years are mostly played with a mod that autoproduces settlers (and workers).