When you research iron working you can plop out the best swordsman unit the era gives. That doesn't sound like a theory to me. One might argue if we are still using jet propulsion airplanes (Me-262) developed in 1943 or are we using super-advanced jet propulsion airplanes. For me personally, the newest Airbus is just a copy of a copy of a copy of Me-262 until something truly revolutional replaces it (like an anti-gravity ship or something similarily impossible as a jet airplane was back in 1943). On relations with city-states, buying tiles etc.? In Alpha Centauri you can do a lot of stuff, or buy everything with energy. In Railroad Tycoon you can do a lot of stuff, or buy everything with money. In Pirates! you can acquire all resources, or rushbuy them with money. In Heroes of Might and Magic you can do a lot of stuff, or rushbuy with gold. In Colonization you do a lot of stuff or buy everything with money. In CIV4 you can produce a lot of things, or simply buy everything with money. In all MMOs you farm everything by yourself OR almost everything with money. ... Or to use CIV4 thinking again: you teched paper, traded around maps, got 1000 gold. Spent that gold on running the slider at 100% science. Developed a new tech, traded it around, got 3 techs and 1000 gold. Then you spent that money to rushbuy a very important wonder. Original investment: Paper. Returns: 4 techs and a wonder.