Dropped like 3 game with the Byzantium since I couldn't use the UA.
And I'd say founding your religion for a cultural victory is extremely handy. If you rely on the AI he might not have any culture benefits in their religion, and it might take ages for them to get here, especially if you're isolated. Actually, if you are relatively isolated, you should really try to found your religion. On Immortal I have yet to take some other dude's religion, although to be fair I used to reroll if I fail at Stonehenge. Now I just don't care and keep playing, I also won't even go for Stonehenge if my capital production suck and just go for Pyramids instead.
But say, if your neighbour is Haile or Pacal or Boudicca, you might as well just wait for them to spread it to you. The founder benefit of your own religion will not be as effective anyways, and that leaves you hammers to make something else.