Yes I think I see what you are saying and I agree. But I am not so sure that it is 100% applicable 100% of the time. What are your thoughts?
No, not a 100%/100% deal, but I think it's common enough to make for a useful hypothesis.
My thoughts: Cultural traditions tend to be built up over many generations and don't usually come out of nowhere without warning. They may have started as a campfire story told by the village shaman, but with the passing of generations the story becomes a facet of tribal identity. Times of strife polarize communities against whoever they see as the enemy, and in those times it's a group's unique memes that become the rallying cry because they help distinguish "Us" from "Them." The winner's traditions may spread beyond the original tribe, while the loser's traditions may be suppressed or die out on their own.
Example: Tribe A worships the lake. Tribe B worships a massive painted rock. The tribes go to war, and the rock-worshippers prevail. The conquered survivors from Tribe A may feel betrayed by the lake that forsook them in time of need, or they may be coerced into becoming rock-worshippers as well, and suddenly there are twice as many people with decorated rocks at their front doors. It doesn't actually matter
that worshipping a rock makes no logical sense; it's a sacred tribal symbol and may persist for generations.
Later on, the rock meme may spawn even more legends, and perhaps even a pantheon of rock-gods and semi-divine hero figures (particularly if the rock people are an aggressive and expansionist tribe who win more than they lose). With the advent of the written word, however, the legends will start getting locked down by whoever controls the writing -- Generally the priest-class and the upper classes initially, as the rest of the population is usually labouring in their fields and doesn't have time to learn such things. The secret of writing may even be forbidden to the lower classes, to keep them in their place. The fluid, malleable oral tradition fades away (or goes underground into children's stories, superstitions or folk art) and is replaced by a more rigid scriptural tradition with a hierarchy. Tribal spirituality has given way to formalized religion, very often sanctioned and supported by the rulers of the land.