First, there is no filler content in World of Warcraft because the content exists in the main story line. Filler is stuff like the G-8 arc from One Piece; the content exists within a single universe and isn't a part of the universe that the main story is in. On top of that, none of the material is ever referenced in the main story, meaning its sole purpose of existing is to buy the writer of the source material enough time to come up with new material for the adaptation studio to adapt. Filler content is not content in between major story lines, it's content that can literally be removed entirely and not affect the main story. Halion is the ONLY arguable filler content, and that's a hard sell because he's a means of introducing the twilight/Deathwing's brood.
Second, the amount of people in this thread and in general implying they can write better than Blizzard is pretty astounding and fairly entertaining. If you can seriously do better than Blizzard, then do it. You don't need to graduate from a top global/national university/college to write, you just need a pen and a medium to write on (usually paper). It's a lot harder for someone to tell someone to be a better animator than Blizzard, or a better artist because that requires specific tools and skill sets; writing doesn't.
Now, am I saying Blizzard is infallible? No; they can definitely do a better job and should definitely hire more writers, especially those who are adept at tying the writing into the actual game mechanics so shit doesn't feel forced like most game stories. I'm simply saying that on a forum where the same thread gets made at least ten times every half hour, people have trouble formulating even the most basic of arguments and a handful of this huge minority of the WoW community can take criticism well, you need to prove that you aren't bullshitting because you can't come up with anything better to say.