I've seen enough fans try explaining a work of fiction to the authors that wrote it that I have doubts that anyone would agree with the "Because the author/dev said so" argument. In my experience, that argument only works when it's convenient. Of course, games are different in that they are more dynamic than novels or movies because the characters in a game are not all controlled by the author(s), so there is a higher likelihood of them saying something different tomorrow than there is for a book/show/movie. In fact, it's pretty much a requirement for games to take character actions and player feedback into account.
Your completely misinterpreting what I wrote and what I wrote supported your position. Arguing against it, weakens that position. .... Simply put, the Lore that exists is there because someone wrote it 15+ years ago. How the game is actually played differs widely from the original expectation. The argument that the 15 year old lore is carved in stone and can not be modified is a fundamentalist thought that rejects the history of human existence. The creators of Ryzom's "pre-history" are entirely empowered to rewrite that history.
To port over to real life ... the earth was flat and the earth was the center of the universe was universally accepted as "doctrine", religious or otherwise. Arguing with that was blasphemy. Then it wasn't, a round earth and a sun centric solar system became the "new truth" .... and now we have Flat Earth beliefs making a comeback, So no.... no truth is static, no lore is static. Even Game of Thrones has tossed "ancient lore" out the window over and over again.
So no... the truth is not static... IRL, accepted "truths" are debunked every day. The second largest religion in the US is "none" (Evangelical Protestant = 25.4% / Unaffiliated = 22.8% / Catholic = 20.8%). This is a substantial change. Was a time when women couldn't vote, certain people could not own property ... acceptable behavior between men and women has changed drastically.
So yes, the "truth " and "way it is" on Atys is constrained only by the folks who make the rules. Granted, it's always best that you follow a logical progression from one state to another ... but there's plenty of leeway there to go in any direction which inclusively works for the greatest number of people. If a % of the player base wants nothing to do with religions, and it's going to be forced on them because "the lore says so" ... simple fix the lore.