Their UUs also are all over the place, meaning you get one slight bonus at one Age and then you have to upgrade and shift to try for another bonus at another Age. All of their powers can either by trivially counteracted (Scouts will make their Spies useless, Supply Wagons will make their attrition useless) or are hail-Mary, last-ditch powers that you really shouldn't be relying on anyway (the 'plunder your own buildings' power is a consolation prize for losing a battle, and worse still, it doesn't actually work on the '+500 All' plunder from your capital). The Russians, in my opinion, are the weakest nation. Their powers overlap nicely, and it's hard to bully or force them into a narrow strategy. The Inca is one of the few nations with direct control over Wealth production. The main limiting factor on Knowledge gathering is Wealth production, and Wealth is gathered indirectly for most nations.
Remember that you can't artificially boost Knowledge production (except with one or two small Rare resources). Inca's gold from mines power is actually very useful.
