Its the best I could findTo me, reliable means less based on luck.
CS and NW are all luck, so not reliable at all.
Yes, starting dirt is luck based too, but that you can tell from T0. How many turns do you give it before giving up on CS quests or settling a NW? Then what if you had just tried three turns more?
Shrine tech is super early (same as what is needed for granary) and if it is third in your queue will get you a pantheon in probably four out of five random Deity games. So that is reliable. With a faith-based pantheon, you will found late most Deity games. So not good enough for OP, but quite reliable.
The only real risk with a scout-scout-shrine BO is that sometimes an AI enhances before you get a pantheon. I hate that!
But I'll say its as "less based on luck" as T0 desert, not many religious civ rushing peity, etc... lots of "ifs" and lucky rolls.
I'd also like to have a reliable method how to do it, but I think there is none. Founding a religion is like building accient/clasical World Wonder. On higher diff levels it has a lot to do with luck.