Flys Gone 2071 said:
1. There is no "Creation and Destruction" theme confirmed. Its just a rumor (if you can call it a rumor, its more like what the fandom wants) with no evidence to back it up.
2. Typing doesn't matter in the myths of the legendary Pokemon. If not Kyogre would have destroyed Groundon and the Water would reign over the Land. Dialga would have beaten Palkia and time and space wouldn't be just 1 whole.
So it isn't necessary for the typings to be equal. If GF wants to make them equal, they do it. If we take examples from the Pokemon myths, it doesn't matter if the Pokemon have type advantage or disadvantage.
PS: It would actually be x4 with Poison and x2 with Flying not x4. Xerneas would hit for normal damage with Fairy type STAB (only Fire and Psychic are rumored to resist Fairy).
1. You are right, there is no theme confirmed. In fact, there is absolutely nothing confirmed about this two pokemon; besides their names, we have absolutely nothing to go on, yet here we are, speculating from the tiny breadcrumbs of clues Game Freak might or might not have slipped for us in what little they have given us so far. So if we shouldn't theorize anything without evidence, we have exhausted the subject with the conclusion:
Xerneas
is (not necessarily lives) in a forest (both in X's box and in the trailer) and Yveltal
is (not necessarily lives) in the sky (both in Y's box and in the trailer). period.
I didn't mean that speculation is wrong but if you use all your arguments come from a speculation with nothing at all from this Gen or previous Gens to back it up, you can't say that the typings must be even. I see the point for them to be even but I don't believe that they put "being even" over the Pokemon's design (of course it fits those types but there are types that can actually fit better). Xerneas could be better Steel, Ground, Psychic than Fairy or Grass but they aren't just going to through the typing just for them to be "even".
2. As I said before, gameplay and story segregation. There are lots of cases out there. If the mechanics of a game and the world it builds don't match, then whatever sense the world might make is lost. If a legendary is opposed to another, but neither of them ever comes on top, despite an objective advantage on one side, I call that bad world construction.
The pokemon franchise has been dragging several cases of this since throughout the years, and only lately they have started to fix some. It's basically the same case of a deus ex machina, where you ask "why?" and the answer is "because."
-"In emerald, why Kyogre couldn't beat Groudon with its moves in the overworld, but if you have a pokemon battle between them later Groudon is KO in one or two turns? "
-"Because one thing is a battle in the overworld and another is a battle with the battle interface"
-"And why is that, in the context of a story?"
-"Because".
That is exactly what I meant. They don't need for them to be even in typing for it to be a "glorious" or "magnificent" or "pair" battle. They can make it a good battle ignoring type advantages (for the story-line/anime that is).
The fact is that yes, GF can do whatever the hell they want to do with pokemon, it's their creation, after all. But if you build a world, with it's own internal rules and logic, and then sometimes s*** (sorry, couldn't think of a better word) all over them, then what's the point of making a world that makes sense in the first place? if they come tomorrow and tell us that now there are 4 stages of evolution, that's OK, it could be explained, but if they tell us that Pikachu now doesn't evolve into Raichu anymore, and that it now evolves into Zapdos, wouldn't make sense to anyone at all. In the first example, they are expanding the rules, in the second they just ignore them.
3. You are right about the typings, but still Yveltal would have 4x advantage over Xerneas with a poison STAB. See above for why that's a bad thing.