So you say that this was the end of the Korra that would use her fists and all, but I think that Korra hadn’t changed that much, but instead has kind of matured in her understanding of what happens to criminal AFTER they are detained.
Eventually she does recoup her fighting spirit (driven, as she often is, by Republic City needing her help)... but first there are those three years of pain and intermittent despair, plus half a season of on-screen struggles and terrible PTSD flashbacks to get through. And even though she winds up in a better place than at the beginning of the season, I think she loses some of her old pugnacity in the process. (Still thinking through the differences between Korra in "Venom of the Red Lotus" and Korra in "The Last Stand"... I'll get to that future entries. ^_^)
Tags: this scene is a tearjerker for me now, and you summed up why perfectly, the audience is saying goodbye too, oh god I'm so sad now NOOOOOO,
The best writing tricks are the ones you don't notice until later, aren't they? ;-)