I just finished The Black Echo book, however it’s not the same story you mentioned. I may be able to see the TV series once I’m back from my vacation.
I tried to analyze the character arc and mystery techniques based on the book. Sigh. The story was pulling me as much as it did several years ago, so it’s far from a deep study.
Here are my thoughts about character arc:
Bosch is considered a loner and got in trouble at work for it. He tries to overcome it and cooperate with Eleonor. However, she ends up to be a bad guy/girl, so his flaw of staying a lonely wolf and keeping his findings to himself is justified. Besides, although many criticize his aloofness, those who counts respect and like Bosch as he is, even if they found him frustrating sometimes.
Bosch is afraid of dark tunnels because of his experience at war, however he overcomes the fear when it’s needed on the job (heroic).
Conclusion: a character can stay flawed if the external forces are against his change and the flaw helps the protagonist to win. It’s heroic/likable/expected to overcome a flaw which could help to save other people (the fear of dark tunnel)
Mystery technique: the bad guy doesn’t need to be a totally bad guy (Eleonor) (it was similar at the Murder on Orient Express, wasn’t it?) and is actually better person than the murdered people and have a good reason for acting the way they act. Protagonist likes/loves the antagonist, so reader don’t even think she might do it.