You clearly don't seem to have any idea of what "canon" means. Anything Blizzard says is God's word when it comes to their stories, no matter how ridiculous it is - heck, people call authors' words (not just limited to Blizzard's) "Word of God" for a reason. Until they say something else, it's the truth. If it conflicts with existing story, the existing story will have to change itself to suit what Blizzard said. It's that simple. Whether it's poor writing or not doesn't matter. Blizzard can say "Hey, Sargeras is a moon rabbit and everything we experienced was just a dream" and that will be the truth (until they say otherwise) even though it sounds extremely stupid.
Not to mention your arguments against Blizzard in this matter isn't even correct. "Azeroth is too far away" is technically NOT impossible. Let's go through it one by one:
- The fact that Aggramar discovered Azeroth, came back to meet the Pantheon, then they came to Azeroth again doesn't really mean anything. There is no indication that Sargeras is where the Pantheon was during that time. For all we know, Sargeras could have been advancing on the wrong direction, and now the Legion would be anywhere between 15,000 and up to millions / billions+ years of travel away from Azeroth. (I tried get a rough estimation of the time between the Pantheon's departure and when Sargeras first found out about Azeroth's physical location
here when Chronicle was just released).
- Secondly, the Draenei never came through space. What are you talking about? They flew in using Exodar. Exodar is a dimensional ship, part of the large dimensional fortress. Those don't fly normally, they teleport through realities - quoting Metzen
Warp-drive, basically. Since Sargeras and his Legion couldn't do that, they had to wait for the portals and summons.