And personally I feel all the rage thrown at him is overblown and unfounded. Every GW game has a character like him. Rurik, Togo, Kormir, Ogden just to name a few of the mains.
Why the shock and anger over Anets well entrenched plot devices confuzzles me honestly. Did you REALLY expect to be "THE HERO"? we the players have NEVER been the hero in any GW game, the story has always been about someone else. That is how its always been and it works well for the lore writers.
Trahearne is more egregrious a writing mistake than any of the other examples you listed. He is the archetypal Gary Stu because he hijacks your story and also is never allowed to fail. The second part is important. Every one else got some humbling through their story, Rurik died and got turned into a revenant, Togo got murderated, Kormir got her eyes plucked out for her hubris and Ogden really isn't even in the same category, he's a side character and a source of dwarf flavored comic relief at times. Meanwhile, Trahearne gets a sword of destiny from his mom after some other guy lost it, he gets to lead the Pact without any major setbacks along the way, and he finishes his epic quest and leaves you to clean up the mess. Not cool.