Agree, and disagree.
Yes, one can get a lot of yields, in aggregate, across the empire. In each of my games, I have completed the ages (including Exploration) by expanding up to my settlement limit (or exceeding by a little) and researched most of the techs and learned most of the civics. In my current game, one of the AI leaders seems really good at getting codices (Antiquity) and digging up relics (Modern). My production and happiness are in good shape; I have ample gold and tons of culture; I'm finally excelling in Science in Modern.
No, I find that I DO need to worry about optimizing yields in my biggest cities. The Exploration Science legacy path requires optimizing, to a greater extent than I have been doing. More than half the time, I have been offered Scientific Dark Age legacies because I didn't manage a single milestone on the path. Overall, it doesn't diminish my chances to win the game, but I do need to better understand this part or I will never get an Exploration milestone.
