[Omnirizon]

I think it's just too hard to really quantify the nations.

there are some obviously powerful nations.
but I can think of ways to counter certain of them with what are considered very weak nations in the same age.

I would almost say that
powerful = obvious and easy to use powerful strategy

that said, some nations are overpowered, but by and large, most of them have options available which makes them all scary in the hands of a crafty player.