Even without the Kremlin, mature towns with both civic boosts beat every production improvement bar State Property workshops.
Also, gold multipliers are available earlier and don't cause health trouble - with a heavy focus on cottages it's often more efficient to give industrialisation an almost complete miss (excepting cities with the Heroic Epic or Ironworks... possibly one or two more for building spaceship parts).
With the Kremlin, nothing else comes close... except whipping in small cities.
Also, gold multipliers are available earlier and don't cause health trouble - with a heavy focus on cottages it's often more efficient to give industrialisation an almost complete miss (excepting cities with the Heroic Epic or Ironworks... possibly one or two more for building spaceship parts).
With the Kremlin, nothing else comes close... except whipping in small cities.