That's fine with the 3x3. I would have done the same.
Eiffel Tower is supposed to be 1 Steel Mill anywhere in your civilization. It is <PrereqBuildingClasses>, not <BuildingClassNeededs>, which is what is used for a building that must be present in the building city. <PrereqBuildingClasses> is mostly used for the National Wonders that require X ordinary buildings before construction, but it is also used for the Guildhalls, Warhead Factory, and Power Receiver. If you really can't build Eiffel Tower in a city without a Steel Mill but you have a Steel Mill elsewhere, then something is wrong.