This is just sad: “a character can stay flawed if the external forces are against his change and the flaw helps the protagonist to win”
If you’re analysis is correct, there is no character arc here. Not unusual for a series, but disappointing when compared to the TV series.
Now, this is not a big problem for the exercise because the goal here is to look at how important story information is presented. In a mystery, that means finding the clues and seeing them in context. (Usually, there are also red herrings, adding to the fun.) I admit that I focused on the bits that led to the ending more than finding the killer in my example, but finding the clues to discovering the killer should be more obvious and easier.
You have some interesting observations, but what were the clues that solved the murder?
My recommendation (not assignment) is that you watch an old TV drama like Peter Gunn. In less than a half hour, Gunn has to find the clues that reveal the murderer. Not a lot of clues. Not a lot of time investment. But maybe there are a few lessons on presenting information. Choose one. Watch it as many times as it takes to be too bored to be caught up in the story. See what there is to learn. https://www.imdb.com/title/tt0051301/episodes It’s free on IMDB.
Or read Chinatown (rather than watch it) and focus on the clues that lead Gittes to or away from the killer. It’s an amazing script with lots more than a mystery, but the mystery is clear cut. You’ll probably care about who killed Mulwray the first time through, so it may take a few readings. I printed out the whole thing and marked the clues along the way. It’s a good practice, but probably overkill.
Here’s a cheat sheet if picking out the clues is difficult. https://www.coursehero.com/file/p3ncen9/In-Chinatown-there-are-clues-that-reveal-both-the-murder-and-Noah-Cross-plan/