In both G&K and BNW, I heavily favor Cathedrals over Pagodas (which beat Mosques, and then Monasteries).
BNW Cathedrals are probably a bit weaker than G&K Cathedrals since the Artist slot was great for extra science (with Secularism) or for popping Great Artists.
However, BNW Cathedrals are still good. I think you are underestimating the art/artifact slot.
1. It's the only religious building to provide potential Tourism (other than through Sacred Sites, which also works with Cathedrals).
2. The slot is often useful. Before Renaissance wonders or Industrial museum, your single art/artifact slot is in your palace. That's it. It's not uncommon to pop 2, maybe even 3 artists in the Medieval Age.
I'm in the middle of an Emperor game (with 13 opponents). 4 or 5 of the AI's went with Liberty, of which 2 of them chose a Great Artist for their Liberty finisher. Even some of the other civs have already generated 2 or 3 artists by Medieval, yet they are all capped at 1 piece of art (which means they must have burned the GA for a Golden Age, or are hiding them somewhere at a different city).
That also means that for the most part, a civ that takes over the capital of another civ, will likely have to destroy that piece of Art since he doesn't have a slot.
3. Even an empty slot is *useful*. Since you can freely move Great Works around, the AI or an intelligent player will shuttle the Great Works around in case a city is in danger.
In the early game, I've found that some civs love to build Amphitheaters. In these cases, it's hard to conquer a Great Work of Writing because even if you take the city (including the capital), the piece is likely to be moved away. Only if the civ has lots of Works of Writing do you have a chance at stealing it. In contrast, if the civ does not bother building Amphitheaters (and some are like that)
Since most civs will only have the Palace slot for Art/Artifact, if they have a Great Work of Art, you know that if you take their capital (good luck

), you will get their Great Work because there is nowhere else to move it.
However, if they have Cathedrals, then they can play the shell game (just like Amphitheaters with Great Works of Writing).
For me, that actually serves as a deterrent to attack. Given the intricacies of the new Warmonger system, I want to be very careful on who I want to attack. Someone with great works, and go gunning for their capital. Those with empty slots available make poor targets because you may need to take a lot of cities (taking a diplo hit each time) to get them.
So in that sense, Cathedrals work as a helpful deterrent in multiplayer and if the AI uses it and you are making a calculated attack. And of course, if you get swarmed by the enemy AI on deity, it's nice being able to spirit away your art to safer cities!
