That seems to be the problem in the civ design. The UB is strange since it requires a lot of effort to utilize it (a) get writing b) build a library, c) create a Great Work) and the payoff is only really needed in one city (the unit production site, besides, creating several great works would probably be too costly).
IIRC GW can be stolen from other civs. I see Assyria having dreadful symmetry in their design - You get techs from taking cities, and when you are it, captured GW gives your units extra XP through the basic scientific building. I see Assyria as well designed.