A major issue for me

She's afraid that although bringing down the Sybil system is the right thing to do, too many people would die and get hurt in the process. She's doing it to protect people. She believes than when the people will put an end to the Sybil system when they are ready.

Basically she is a very very very poor kind of objector and pussy-footer with what is clearly a sugar-covered DICTATORSHIP (where the wrong thought in people's heads is a MAJOR CRIMINAL OFFENSE!), if it wasn't for the System's psychotic brain-jars playing with her for their own amusement, she would have been executed/jailed for treason a long time ago.

especially since she has a degree of immunity to these "Symptomatic Scanners" similar to Makishima (but not quite on his level)

Because if she brought down the system she would collapse the entire government, and would be resposible for tens of thousands of deaths. She knows the Sybil system is unjust, and if she had the means to bring it down without resulting in consequences that are impossible to predict, she would surely do so.
It may not be right to allow a cybernetic system to continue its enslavement of the populace, but it is even worse to knowingly endanger the lives of an entire country. You may not care about the lives of others, or at least the fictional lives in this world, but she lives in that world and the people are real to her. She is not a murderer.

First and foremost, I didn't understand why the "true" form of the Sybil system was so shocking and made the whole system undesirable. Why was it ok for an automatic system to control and organize people, but it was not ok for it to do so if it consisted of a bunch of human brains? It was not even an oligarchy, since those were not human beings anymore, they were much more like the Borg from Star Trek, collective-human-machine hybrid, with much of their personality features toned down or even vanished. I for one was actually quite impressed with the notion that no pure machine can judge correctly the behavior of human beings and come up with fair verdicts. I was also impressed with the notion that the brains composing Sybil had belonged to people the system hadn't been able to account for, and thus could have an external perspective on the whole situation. I also liked the fact that they had been very different individuals, this being able to cover a large array of human attitudes, features and general information.

Whether it was right to have the system the way it was, controlling everybody's moods and thoughts and making decisions for them, is of course debatable. What I don't see as debatable is that brain-Sybil was more scandalous than AI-Sybil.

But then, I have only watched the first season of this series. And I don't see myself moving forward because, as much as the ideas were interesting and the development surprising, the main characters were terribly bland.

Makishima was somewhat interesting, with his crime coefficient (CC) never going up while committing murders - and here we can speculate that this happened because CC measured an individual's stress level or probability/propensity to commit a crime, while Makishima was never stressed out and his intent to kill could never be approximated by the system. He was in complete control of his emotions and his will was the only trigger for his crimes, his intent to kill was never a reaction to something, and the system was unable to measure pure will. But he vanishes from the series after the first season.

However, Akane's CC was always low simply because she never intended to kill anyone. She's ever the perfect pawn of the system, and her anger at discovering the brains room felt totally artificial. I never had the feeling that she struggled to decide anything, she never in any kind of moral or psychological danger, what's more - she's the living proof that the system cannot be too bad, if it can produce something like Akane, or if it can accommodate Akane so well.

So all in all, she could be so forgiving because she was the perfect component of the social system designed by Sybil, and as such her reaction could never have been any different. What's annoying is that we're supposed to believe that she struggles to reach her final choice, and her character in general.

there's a highway that is curling up like smoke above her shoulder