But it has not yet been discovered? I mean, it is quite possible, knowing the constantly evolving list of monsters, as well as the technology level increasing (very) slowly over the course of the series. I don't see why there COULDN'T be an elder dragon stronger than Fatalis. And, if they decide to create one that was strong than any of the three variants of him, then hopefully they would actually make something that actually manages to be threatening very well and actually isn't so danged generic looking.