Tallis is a self-insert which is creepy. It's like bad fanfiction where someone from the present gets magically teleported in the amazing world of Dragon Age and get to be all awesome.
Obviously then, you aren't aware was a collaboration between Gaider and Day from the very start. A collaboration suggested by BioWare, not Day. Whether it was Laidlaw, Darrah or Gaider, or someone else, I don't recall.
From what I do recall from various interviews surrounding the web-series and the DLC, she was reeling from the shock of being approached for it for quite a while. Tallis as a character was conceived by Day, but the rest was a collaboration. Like or dislike the character, but give credit where it's due: the initiative was from BioWare.
I can agree that the DLC ended somewhat ...off-key, but that's a minor issue. As for Hawke being a "just a bystander," or whatever... Well, no more so than the rest of DA2, barring perhaps Legacy, and I'd disagree emphatically on even that. And I'm not even going to touch into the apparently incessant need to kill every character they don't like.