Sorry I'm a little late to the discussion, but I've been pondering the various points.
First, I think it might be beneficial to note that there is a difference between FATE keeping El Nido (and in turn, Elements, Dragonian Technology, and any Chronopolis technology that might be laying around) from influencing the timeline and Fate keeping El Nidonites cooped up on the archipelago. One does not necessitate the other; indeed, it is entirely possible that keeping the El Nidonites cooped up would have been counter-productive for FATE. If word gets around that no one leaves El Nido, ever... well that attracts attention. Consider the real-world Bermuda Triangle: it is no different than any other patch of sea, but it has a reputation, so people specifically visit it for that reason. If FATE never let anyone leave, it might affect the timeline more than if it did let people leave.
The question then is, to what extent might FATE control the events once outside El Nido. It seems like it would have been simple enough for FATE to preprogram General Viper and the others to keep their elements a secret (or, even if not a secret, in some way to prevent the mainlanders from getting too interested). Of course, FATE would have also had the power to convince the Acacia dragoons just not to take elements; the impression I got from the Four Divas was that it was their innate fighting prowess, not their use of elements, that made them famous.
Random aside... if we are to assume that elements might have been exported to the mainland, might not at least one or two Records of Fate been exported as well? It not, why not? But if so, wouldn't that possibly extend FATE's influence (and in turn, extend FATE's abilities to prevent changes to the timeline)? Could FATE then be controlling not just the El Nidonites but important figures on the mainland (as presumably owning a Record of Fate would require wealth and wealth usually translates into power)?
Radical Blues, while Viper and the others might not use the Records of Fate, it should be noted that such devices exist inside Viper Mansion, implying that some of the Acacia Dragoons do, in fact, use them. Given that they've been in the area around 100 years, one would also assume some degree of intermarriage as well. I suppose it is a question of how much the culture of the area influenced them. Perhaps I am wrong, but it would seem like using a RoF (not to be confused with ROUS's) is enough to get one "hooked," so even a random "sampling of the local flavor" would have drawn the Acacia Dragoons into FATE's computery clutches.
