If you just mean that she violently ended a war...
Look, I feel in the whole "Oh, korra is a hotheaded thug" thing, we've kind of forgotten
the reason that it's bad.
I'm not opposed to an avatar (especially one that isn't Aang) using violence as a means to resolve a conflict. The situation with Kuvira, if Korra had gone out and tried to reason with her using actual reasons, and especially if Kuvira couldn't provide good reasons for why she was doing this except out of pure hatred for Suyin or whatever, then I would have absolutely no problem with Korra shrugging and saying "Well, I tried." before going Avatar state on the whole army. But the Kuvira situation is just badly written because we don't have much reason for why she's doing what she's doing.
Compare this to Kyoshi's sitaution. First off, we don't know much about Kyoshi's character, but in every portrayal we see her, she's calm and collected. When Aang contacted her about Ozai, she simply said that he must do his duty as the avatar. That's what Kyoshi is characterized by, her commitment to doing her duty as the avatar. She does not seem inclined towards violence. Meanwhile, Chin is portrayed as a stereotypical tyrant that's trying to conquer the earth kingdom and even wants the avatar to bow to him. He's just a generic bad guy. Could their be more details to their encounter than we know of? Of course, we only get a brief summary of the event from Kyoshi.
But given that this is TLA, where we usually have well written and justified conflicts between groups of people, given Kyoshi's general demeanor, and given the brief characterization of Chin, I'm not sure I see a reason for why I should object to Kyoshi doing what she did. It's not like she intended Chin to even die. She just decided that his conquest was not right, so she moved Kyoshi offland so that he couldn't conquer it. Chin died because he fell off while this was being done. She didn't really care that she killed him and considered it for the best, so whatever.
Compared this to Korra in the past. Her immediate reaction to every conflict was to beat it down with violence. She saw the world as very simple. She was a good guy, they were bad guys. Beating them up is not just what she's supposed to do, but it's something she loves doing. She loved fighting and violence. The reason Amon is as much of a failure as she was is that Korra never cared about the equalist conflict. She was just looking for a villain, and Tenzin would be the one to handle all the boring sociological stuff about if nonbenders are being treated fairly or not. Same with Unalaq, she only cared about learning about spirituality insofar as she needed to kick Spirit ass. It was especially obvious in the finale where she just choose to keep the spirit portal open. She didn't give any reasons for why she thought it was a good idea, it was more of a "Hey, why not" sort of thing. And the show goes along with her line of thinking. Meaning, when Korra doesn't give any thought to the equalist conflict or decides that keeping the portal open on a whim is a good idea, the writers do the same. That's why no one calls Korra out on her inconsideration. That's why no one asks "Hey, korra, WHY do you think it's a good idea to keep it open?"
And then came Zaheer. He was one step forward, two steps back. Before she met Zaheer in the spirit world, she was completely ready to throw down with him as soon as she heard he was an enemy. THat's all Korra needed to know. But then they talked in the spirit world, and he gave her his reasons for why he was doing what he was doing. At that point, Korra had to step back, because she couldn't classify him as just Baddy McBadguy at that moment. And it would have been great in the writers pursued this, but they instead opted to focus on Zaheer's viciousness. His team attack Korra while she's resting, and he is willing to hurt the air nomads, including children. And then he explains he is personally going to kill her. Even if his philosophical leanings might have a point, the position he puts Korra and the others in don't really leave any breathing room for moral ambiguity to flourish. So, aside from that ONE MOMENT in the spirit world where Korra makes a pathetic attempt at resolving this through talk (mostly because she isn't good at that stuff), he's essentially Baddy McBadguy even if he might have something worth while to say.
So then we finally come to present day. Korra is trying to do things diplomatically.
These posts explain why it doesn't work pretty thoroughly.
So where am I going with all this? The reason that Korra is a bad avatar isn't that she's violent. It's that she's just....stupid, and her default inclination happens to be violence. If it happened to be evasiveness (like Aang) it'd be just as bad. What seperates Aang and Korra is not their personal inclinations, it's their (and by extension, the writers) ability to reflect on the world. In the first two seasons, Korra just sees herself as a good guy without giving any thought to the larger sociological/political/moral/spiritual issues at play. As far as she's concerned, she's just the weapon that puts down anything that threatens whoever she sees as the good guys, which is usually based on their associations with her. That's how Tarlok and Unalaq convinced her to join them. "Hey, we can teach you new ways to fight" and that's enough for her to become their agent. She had the opportunity to grow in season 3, but that the way the situations were written didn't allow her to grow by reflecting on the moral questions that Zaheer presented. You can't ask someone to honestly debate the merits of your philosophical position when you have a gun to the heads of their friends and family. And now we have Kuvira. Yeah, Korra wants to be reflective now, and try to see the moral complexities of the situation, but this fails because the writers can't seem to write intelligent polticial debate. There are potential points that could be raised.
I suggested them myself. But Korra doesn't bring them up. Suyin doesn't bring them up. Kuvira doesn't bring them up. No one brings them up, presumably because the writers haven't thought of them, or else I don't know why they wouldn't include them.
Of course, I have to emphasize: Korra being stupid is a symptom of the SHOW being stupid. I don't know who headed writing for TLA, but whoever it was was intelligent enough to understand the various political and moral implications that situations like that held. Whoever is writing Korra...don't. They just don't. They've definitely heard the complaints. They know moral reflection is something Korra needs to do, but they don't know how moral reflection itself works. So we get the epic confrontation with Kuvira that goes "Uh...you should stop this because it's wrong for....reasons. " "you know, I had to make a lot of hard choices in the past. Hard choices I am not going to specify or explain in any way." "Still...back off?" "You and I are a lot alike, Korra." "Yeah, because we both fight....like pretty much every other main character on this show" "Right, therefore go talk to Suyin to get her to back down. I won't do anything while you have your back turned. Pinky swear. " "kay".
This isn't anything like Roku or Kyoshi. With Kyoshi, we don't get a lot of details. It may very well be that the situation was much more complex than what we got, and it may be that Kyoshi acted wrongly, but based on what we did get, Kyoshi's actions were are well justified on both a character level and thinking level. With Roku, it was a mistake to let Sozin live, but he had good reasons to let it go at the time, and Sozin only did what he did as a split second decision DECADES down the line. There's no way Roku could have predicted that would happen and all the moral implications of having done it are well defined in the minds of the writers because even the characters debate this. This just isn't the case with LoK. The writers here get an idea that has potential for a lot of moral conflict,
but they never do anything with it. That's what makes Legend of Korra so much lesser than TLA. That's what makes Korra an idiot in the face of Aang. The characters have to be able to reflect on the world around them in deep ways, and the writers just seem incapable of that. Had TLA been written by these guys, we'd have the same issues, just in a different way.