Sorry for asking but how does the swap cities work? I put one warrior on each to swap (all requirements fullfilled) and they became immobile for at least 17 turns with no effect appart from that...
OK, I started on forested prairies with lots of corn, wine, furs and deer (wildmana map).... but I had 3 cities before any enemy had 2 (prince difficulty) and 5 before they have 3; even when many wolfraiders and deers attacked me.
The thief founding cities is extremely unbalancing imho, because your cities still can grow while constructing the "stablish new city" mission. You could make it cost more hammers (and turns) than normal colonizer, instead of less.