That was a great write up. However I remain unconvinced that religion, apart from minor bonuses, allows you to win more easily, esp compared to adopting someone else's or even ignoring it. I can and have seen short-term bonuses (like the extra units holy warriors can provide) but not sure about longterm benefits apart from generating faith for Great Persons. That was what I meant by diminishing returns. I think it's a great addition to the game but I believe its opportunity cost/benefits are not that great.
Tithe +1 gold pr. four follower. It's TOTAL followers in all towns divided by four. It's millions of extra gold during a game, same goes for culture or whatever bonus you pick. It's insane amount of bonuses, even if you have to "waste" time building faith buildings. (Except for a faith civ or with a natural wonder, where you get the faith for free.)
Have your resting point with citystates be friendly... Huge map defauls to 24, so 24 citystates giving you at least friendly bonus, some allied, since you can't avoid completing some quests once in a while with that many.
Combine expanding border, with russia and wonder and have your towns area cover max range. (All your towns Six titles from center I think?). Combine it with the great wall and anyone attacking you is doing slow motion dance towards any of your towns, you can prolly build an army to defend before they arrive.
Diplomacy bonus, have that big bad neighbor, be your best friend for the entire game. While you OOC an insanely easy culture win.
The extra possibilities is endless with all the options religion comes with.
Do you need religion to win? Uhm, no we won in vanilla without religion and the AI doesn't play religion well enough to hurt, but that's a silly point. The question should either be, is it easier to win with religion and/or is it more fun.
As I understand the game both is true and that brings up a breaking point with the difficulty level... You only have a short window for religion starting in the early part of the game, since the AI get bonuses on higher difficulty levels, it kills any chance you had of racing to compete. You might as well just enable ancient ruins, it's total luck if you get a religion and total luck if you get any good options.