We're not "attacking" a "pillar" of the cosmology, we're defending a neighbouring plane that happens to be the destination for the souls of the dead.
The Tolkien comparison wasn't meant to say it is exactly the same thing, WoW is closer to a comic book universe where many people work on it over many years (although Tolkien wasn't averse to the odd retcon as he merged his greater mythos with the stories he used to tell his children.) I was pointing out that most people are familiar with The Hobbit and The Lord of the Rings which are fairly grounded fantasies but that doesn't mean the things described in the Silmarrilion aren't equally valid despite being much grander with abstract concepts given forma and a more spiritual angle to some of the ordering of the world.
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In what way? The core gameplay is the same as it pretty much always has been, the graphics are to a higher standard, the major pillars of gameplay like dungeons, raids, battlegrounds, arenas and a large open world are still there. Closest thing to mobile-friendly gameplay is the missions table and if anything that is much less important than it has been in the last few expansions.