Das Capitolin
Warlord
While troubleshooting this issue, I have determined that an issue exists in the lua code for all versions that (almost always) grants a Settler unit to AI capitals when starting a game in later eras. After spending several hours testing and tweaking, I am unable to resolve the issue. For now, it seems that only Ancient era starts will prevent the AI from having an additional Settler (unless set to Deity difficulty).