I hadn't know about this thread till recently, but I myself was noticing a lot of similarities between the trio myself, to which I posted a few brief observations in other threads. The initial write-up here is certainly more detailed in its focus, so thats certainly helps get positive/any feedback at all pertaining to the discussion.
Effectively, I would say that the stories themselves from a westernized perspective are largely the same. While my genre and medium samples are relatively limited, even more so since I rely on english translations, but I've been studying several japanese stories presented through manga and video games, and frankly, they just overlap a lot. The jokes and tone and drama effectively are also all the same too, with some fluctuation based on who is writing. To me these sort of overlaps are intentional as a mix of cultural style and marketing technique.
While Jormungand is correct in there being some base differences between Dues and Lavos, that's simply part of the setting of each game. One choses to emphasize creation through a religious perspective (and the use of religion is heavy in Xenogears) while the other takes it from the evolutionary/scientific perspective, and then they have their settings consistent with that perspective. With the understanding of their tone set, the two games I find are very much so parallel. Even FF7 fits into the mix, but from more of the animism perspective.
