Thanks! So, if I dont found a religion, is the only thing I lose out on is a founder belief? (And those tend to be of pretty marginal benefit with all the AI missionary/GP spam.)
Yeah, you won't get a Founder, an Enchancer or a Reformation if you don't found. But most Founders are not that hot. The best ones in G&K were Tithe and Ceremonial Burial. On Tithe, religion Gold was nerfed due to over-availability of it elsewhere. For CB, Happiness was nerfed via going Wide being nerfed, on top of it being nerfed by half directly. For enhancers, you don't need most of them if you don't have religion to spread, obviously. And finally for Reformations, you shouldn't have a problem founding if you opened Piety.
On top of that, Religion in this game is funny in that some beliefs apply to your religion, other beliefs and policies apply instead to your empire, while some of both apply in their own unique ways. All while not mentioning in the tooltip exactly how they work. And so yeah, I've found that beliefs that require your religion or followers are generally overrated due to the common assumption that early Missionaries plus a good passive-spread enhancer is enough to keep control. This mentality must come from lower difficulties on gamed starts, because in most of the games I've played, I've been Prophet bombed 2-3 times by each nearby Religion. After a while, I just bought one Inquisitor to sit on the Holy City and let the Follower beliefs come and go.
Since in the end, Follower beliefs that unlock Faith purchases are extremely good because they function to full effect even in a brief window. That's basically all the Religious buildings. Compare Pagodas to Religious Center, for example. Not that Pagodas isn't seen as the best ability, but the AI values Religious Center pretty high, I've noticed. Pagodas cost Faith, but they re-earn it. Also, followers like Divine Inspiration, Religious Community and Religious Art are underrated because they provide nearly all of their benefit even while restricted to your Holy City only. Then when you get a buliding Follower from an AI religion in a border city, you take advantage of that window to Faith-buy. I would even consider buying Missionaries of an AI's religion to accomplish this while I own my own, particularly for Mosques, Pagodas, and a Monastery in any city with Wine/Incense. You'll have earned the Faith back by Industrial where you start to buy GP's, and you don't need your own religion.
Founders and Enhancers are where I think most people go wrong, though. Initiation Rites and Interfaith Dialogue are the best on higher diffs, imo, because they don't depend on spread. For enhancers, I think RT and IP are not very good, while a lot of the community values them as the best. I prefer Holy Order or Messiah. In fact, I am pretty sure both Messiah and Reliquary function at 100% even if your Holy City gets wiped out. Messiah is my all-time favorite because I just plant Prophets, pick up the New Deal in Freedom Ideology, and hopefully have Glory of God or other good Faith dumps.
Reformation beliefs I have not been able to figure out fully. Some of them seem to apply to your empire, not your religion. Charitable Missions does not even seem to have anything to do with Religion, at all. But the best for most cases though, imo, is Glory of God, which at worst requires you to have at least one city of your Religion, a condition you can easily fulfill. In fact, you probably don't want to waste much Faith on active spread with this belief, if at all in BNW. Purchasing GP's seems to be one of the only VC-related uses for religion, in the end. It used to be useful just for building up empire size, but empire size is not as important in general with this X-pac.
Short version, steal all the Faith buildings you can, FPT >> Founder spread, and neither Stonehenge nor founding a religion yourself is necessary for the GP's you should be using your Faith on.