It's a sad inevitability that the common reader would want to see the main character slaughtering people all throughout the story, regardless of the plot, themes and character development. I mean this is why manga like Bleach are so successful, they satiate the reader's bloodlust, the need to see endless battles and special techniques and catchphrases.
Vinland's not that kind of manga, just roll with it peeps. Planetes wasn't your casual sci-fi manga either.
Sure it was fun seeing violence in a historial setting, but there was always context for it. Thorfinn was never a typical battle manga hero, he was presented as a vague character treading a thin line between tragic victim and menacing aggressor.
So basically some of you guys have no right to act surprised or disappointed at the turn of events lately. The direction the story is going in was on the cards long ago. Admittedly I thought Thorfinn would actually get his revenge before realising how pointless it was, so kudos to the author for robbing the character of even that.