DA isn't a given, it was whatever the creators wanted it to be, and still can be whatever the creators want it to be, so... I'm not sure that's really an issue.x
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It IS an issue when writers/developers work for years to establish the world (through games, books, comics, etc) and then stop caring about its internal consistency whatsoever. That's NOT how effective storytelling works. You can't just introduce things on a whim, especially if they don't fit the established world at all, just like you suddenly don't add the fifth wheel (mounted sideways) to a car.
I mean, it would be as silly to try and force-introduce the magic system from DA into Fairy-Tail. I mean... what for? It makes no sense.
They could adopt a full blown anime style tomorrow if they wanted for DA4 or something
No, they wouldn't and both you and I know that if suddenly DA4 was released in a "full blown anime style", people will be screaming "BETRAYAL!" or at least asking "Where the hell did that come from?".
I mean, they can have an anime featurette or maybe even a separate short story - they've done that already after all with "Dawn Of The Seeker" didn't they? (from what I heard, it doesn't have a good reputation).
But adopting anime style and - to be more specific - bombastic and over-the-top style of drawing or storytelling of Hiro Mishima to a main game with its continued story-line or plot elements, for no rhyme or reason, would be a recipe for disaster.
Also I don't think there's necessarily a big difference between Western and Japanese takes on fantasy if you compare something like Berserk to Game of Thrones they obviously have differences but they're invoking similar ideas at the same time.
Berserk is unique, even among anime. But even if Berserk is similar to GOTY compared to OTHER anime, it still is told in a Japanese way. Mind you, I'm not saying that it's a bad way - just different. Detail-wise, they focus on somewhat different elements, different ways of telling the story and different things that matter for target (in case of Berserk, Japanese) audience. There are too many differences even between Berserk and DA, and many, MANY more differences between DA and FairyTail.
In fact you just said it yourself, Fairy Tail seems to have superhuman abilities like superman..... so... like American comics.
.... That's not a good enough reason to introduce it to DA
Like, AT ALL. As far as we know there are no Superman-like superhumans in DA, nor there's any indication that Superman-like beings wouldn't be anything other than lore-breaking.