I totally agree with you on every point you've made. The MC is pissed, and it is seen that she deals with her anger by boxing so it makes total sense for her to go about looking to beat up the criminal. There's no point in going to the police who have already made it clear that some of them blame her sister for what's happened to her. Why go to people who obviously don't seem to care about the situation and aggressively dismiss it as her sister's fault? Regardless, she doesn't seem like the quiet type in the first place, more like a woman taking matter into her own hands, literally.
Your second point is also understandable. I don't know what people mean when they say she's losing to men, when she's only lost to two dudes thus far, both being trained in martial arts and boasting a size difference. Not to say she can't beat them eventually, but she's only been in the ring and the outside world is vastly different from a boxing match with rules and regulations. She has been seen beating up many untrained delinquents and rightfully so, but her losses so far don't seem to be unreasonable I believe.
Exactly, the character isn't badly written by any stretch of the imagination. Her dad called the two sisters trash, her uncle clearly doesn't give a damn about the two, and her aunt apparently wasn't all that supportive either. She's a kid, all those years of abuse, and negligence lead to bad tempers, and getting into fights. At least she went to boxing, and didn't choose a path like her sister's.
When it comes to her losses, I think everything has been said already. I've had boxer friends who tried sparring with different martial arts like kickboxing or even friendly matches against street fighters. The first thing they notice is that they are clearly outmatched in the kicking the department, and that they can't rely on a ring's boundaries to push their opponents against the ropes so they can stop moving. At least from what I've seen, she has to be extremely good at adapating, I mean she took her skills, and adapted them well to the streets. She isn't surprised about weapon attacks, kicks or attemps to grapple. She dodges them...something most boxers would probably not react to so perfectly, since they don't face those kinds of attacks.
Yeah, that's very confusing to me too. It seem like the narrative being told is that the author is trying to make this strong women a punching bag for the men she fights, and that's simply not the case at all. All her losses were justifiable and everyone she fought understood that she was quite skilled in fighting although still lacked in experience. As Jman95mf mentioned earlier, she's adaptable and I am pretty sure she is going to better herself, train differently then she has in order to succeed. Besides, why make her strong to the point where she can't lose in the beginning? What's the challenge in that? I love me some OP characters, but in the setting that the author has made, her whooping everyone's ass off the grip is unrealistic.
From the previous posts, I've seen one person was critiquing the story for being too focused on the "fighting" aspect, when this is clearly a fighting story, and the character has been constantly trying to find the truth through ANY means necessary. Why would she care about a boy who's got a few hacking skills if all she wants is to fight? Why would she go to the police or search everywhere for clues if the plot is just fighting? I'm not defending the author by any means, he could take the story elsewhere, but it's realistic in the sense that a damn high schooler isn't going to turn into detective conan and figure everything out with 0 evidence and support.
Another post mentioned how the "girl" was losing against men. They're two times her size in most cases, and the one guy she lost to, was really fucking buff, had tons of experience with fighting, and knew how to read his opponents. I'd like to see any man go up against a guy that is 30kg or something of the sort, heavier, and see how they fair if that guy has more fighting experience. She's an amateur boxer, he's a pro street fighter who clearly has gotten his hands bloody several times. Why would she win against him if she has so many things against her? Experience could make up for some of the weight difference, but you can't tell me it's the author making "the girl lose against men", when she has less experience than the guy, and she has half his weight almost. That makes no sense, and if you'd ever compete professionally or gotten in a fight, you'd know that she would lose 8 out of 10 times.
....rant over