I can see how you would think this is confusing. Yes it is very violent and should probably be a YA book, and yeah, some parts are not the most appropriate.
I do agree with you that Tris however is not a good role model. She get's recognition because she had an aptitude test for 4 out of the 5 factions. I have to agree that she is not the best of role models. But I can see how people can agree with her. She is not a hero as most people in books are. That may be why she isn't a good role model. She is not incredibly smart, strong, brave, kind, or anything. She is just an average person. People sometimes read books because they want to get a sense of someone different, and when you come to this book, you find a main character that's just like you or me, but living in a dystopian universe. That's why some people like this book because they see themselves in Tris. I know that sounds super corny but it's true.
I also understand the Dauntless situation. Dauntless isn't like the rest of the factions, and Veronica Roth, I think made it that way. She wanted Dauntless to be different. She wanted to show that while there is peace, and harmony in the world, there are also people like the Dauntless, who are violent. That is basically our world now. We are not looking at something that is different than our world today, we are looking at the same thing, just set in a different time. Think about how separated they are. They have a choice of what trait they want to be known as. The selfless, the smart, the brave, the peaceful, the honest. They can make that choice.
Why I really like this book, is because of the concept. There are other books like the Hunger Games, which I love but it is a world where you don't make a choice. You are stuck with what your stuck in and theirs rarely something you can do about it. Divergent however you have a choice. You can choose your faction. Tris chose Dauntless, because she wasn't honest enough to be in Candor, she felt that compared to her brother and her parents, she wasn't selfless enough to be in Abnegation, and she didn't want to be in Erudite because of her fathers grudge against them. She didn't see a point in going to Amity. Her main choices were to stay in Abnegation or go to Dauntless.
It's a unique idea, that hasn't been placed in a book I have read before. I think that it is a type of book you either hate or love. I don't think Tris is the best role model and I think the story line can get fuzzy, but I think it is a unique concept, and you should read the series. And in my opinion the second 2 are better.