Are you implying that G&K provided a credible wide Cultural Victory strategy? Do you think the culture yields from the Religious Beliefs are significant enough to justify building more cities and raising the next social policy threshold? Im not trying to be argumentative; Im legitimately asking. Maybe Ill have to experiment with this in my next game (although it looks like Id have to play France again).
Apparently the math is that as long as you have full culture buildings and specialists filled, additional cities will always speed up policy acquisition. The struggle is the later the game goes, the more difficult it is to drop a couple thousand gold to instantly rush-purchase all the culture buildings.
I think it is one of those things that on paper it looks viable, but when you try and apply it in-game, it just doesn't work very well and it is easier to just stay smaller.
Of course, large puppet empires are a viable strategy when going for culture, since puppets don't increase policy cost.