I am defensive about this because that is my #1 criticism I had with vanilla and G&K. Too many games (immortal and emperor) where I have seen the AI opponents not trying to win when they could have. These included never seen an AI win culture and simply stop winning space or diplomacy. And I have seen large AI armies just sitting there. (Even having an AI I early DoW or sneak attacks can be effective in slowing you or a runaway down, if nothing else.) The results, oftentimes, is a hollow or unsatisfactory victory - as in no way I should've won this game. There have been exceptions, when I played occ and was next to Greece and a deity game next to Aztecs.
But I have seen an invasion force off my coast just sitting there; AI spaceships part just stop building or not assembled; defenseless AI wonder cities; AI units moving out of a capital when I approached; large AI forces on my borders while I'm scrambling to get parts built; and AI stop getting city-states and become passive when they could've easily won diplomacy.
Now there are more mechanics and allegedly, they're not using them to their advantages either. That is wrong. It doesn't have to be military (even though that should be their easiest way if they have the gold). A good game is one where you win (or lose) by making good decisions in the face of like opponents, not in the face of passive opponents that are handing the game to you, in a manner of speaking.
Now I understand your point better; we were on the same page after vanilla release, remember? I was fierce in that respect, in fact, earning myself a lot of trouble in this very forum. Why do I tell this? Because the only thing no one can accuse me of is complacency.
With that said, I don't know what is going on with your games of BNW, but I am not seeing what you allude to in mine. I am not seeing passive opponents as in "immobilized", but more cautious AI opponents that may or may not become more competitive in the mid-late game because of that. I like that, and I find it makes for much better gameplay, including war-oriented gameplay. What sense does it make to have completely aggressive AI's right from the start when they cripple themselves for the rest of the game by doing so? That's exactly what it was before BNWAI; let's be honest. Who couldn't win an early war against the suicidal AI pre-BNW? In fact, it was a certainty, you just needed to know that they would come, and prepare yourself just enough to be able to hold their suicidal rush but still presenting a target of opportunity so that they would carry on with their early suicide plan. I never found challenge in that. Once the initial suicide was over, the whole mid-late game was yours. No challenge.
What I see now is the opposite. You can feel the AI considering a lot of options (the lot that was hugely increased by BNW). You can see them struggle with the human player for early gold, yet they manage the scarcity well; same with happiness (AI really learnt how to deal with their unhappiness, thus the decrease in semi-cheating bonuses in this regard is completely justified). They really build up trying to be a better opponent for the rest of the game, and not only a fake one for the early game.
Perhaps you need to go longer in your games, or play more, if you did not so already, to see the true evolution of the AI's early decisions? I am seeing that (of course, it does not work for them always, as it does not for the human player in many instances, and that is the challenge), and I like it.