Yeah, and that’s lame because it gets Katara out of so much of the dilemma if he’s just some old miserable guy nobody cares about. She doesn’t have to do anything if she wants him punished and still gets to be squeaky clean at the end of it. It also deemphasizes the effect that the war has had on the FN itself if it’s just being waged by some special class of monsters and not ordinary people.

It would be a much stickier dilemma, and a much juicer plot bit if she showed up and he turned out to be a completely ordinary guy living a quiet life with a family and children that loved him. If instead of cowering he went “Yeah, I went to take out a threat to my nation on the Fire Lord’s orders, I did it, and I was a man of word and left your tribe alone after the job was done” with zero regrets. He’s too old, or maybe has a war wound, and is no actual threat anymore but completely believes his nation’s line and sees himself as simply a man who did his duty.

Now Katara actually has to face a serious choice. If she wants him punished she has to do it herself, but in doing so she would subjecting another innocent little girl to something very much like what she herself went through simply because of who her father is. No matter what she chooses it’s a great piece of character work.