I know this is gonna be a cop out answer but anyway...
You will eventually see a pattern in style when you play a game long enough especially when you come accustomed to that writers style, or in terms of writing style, that it could become repetitive.
WoW does have its fair share of cliche's like most fantasy when it comes to writing. WoW has always been that way, hell, Warcraft has always been that way. Warcraft has always been super over the top, bombastic, in your face, in its writing style never the type of game to deal in subtly. "THE EARTH SHALL TREMBLE' or 'THIS WORLD WILL BURN' 'THE BURNING SHADOW HAS COME TO CONSUME US ALL' that type of over dramatic silly phrases are just common for the franchise. I think thats just apart of the charm. Its very in tune with what Warcraft is. Just look at Warcraft 2 or Warcraft 3 you'll notice they over use certain phrase to get a message across.
ITs less about how the dialogue is overused, but how it's been presented, how its always been presented. To me Warcraft has always been Saturday morning cartoon levels of writing, and that isnt bad at all, it has its morals and lessons, but is also interjected with so much cheese that when you get older you sort of come to love that charm.
The dialogue in WoW is akin on levels to something like Disney's Gargoyles, or he X-Men cartoon. Maybe even going as dark as the Batman animated Series. Even those awesome shows had cheesey dialogue. WoW is a cartoon in that aspect so the dialogue reflects that. Once again I know people are going to be insulted by that but I think that holds up more in favour of how good Warcaft is not for how bad.