I think that one of the reasons why people misinterpret Wylan's character and arc, among others, is because they misinterpret the relationship between him and Kaz. This post has kind of mitosised off from the BFWP (Big Fucking Wylan Post) I'm writing because it's a bit of a different focus and constitutes its own post.
A lot of people talk about Wylan's character and development as though it's meant to match Kaz's - starting out as a nice kid who the city forces to become amoral, indifferent to violence, and well-versed in crime. These qualities are usually talked about with a weird reverence as an irrefutable symbol of "badassery", as though it's always a positive development for any character regardless of the story's narrative, which annoys me but is not the topic of this post. That's part of the BFWP's job.
Following Kaz's exact development is not the point of Wylan's character. The point is that Kaz and Wylan narrative foils - very similar in many ways, but with a fundamental difference that creates the "broken mirror" effect/shows how they could have turned out if they'd chosen differently. I think that difference is how they respond when they climb out of the harbor after their respective betrayals. Narratively, Ketterdam represents a very harsh system that presents the people struggling there with very few options. You can either choose to ditch decency, play by the Barrel's rules, and live, or you can hold on to decency and die.
When Kaz returns to the streets after Jordie's death, he chooses the first option. He copes with what happened through ideas of revenge, and to survive long enough to see it he quickly turns to thievery and violence. He thinks to himself after he robs a kid for money and food that it was much easier to survive when you've left decency behind. He survived through violence, creating the Dirtyhands persona around himself for protection.
When Wylan has to fend for himself, he choses the second option. He finds "honest work" at the tannery, where they exploit workers and expose them to toxins. He wonders if he'll live long enough to use his savings to leave the city, or if the chemicals would kill him first. He was smart enough to steal and survive, but he chose decency, and with it, he chose death. There are a number of reasons why he chose differently than Kaz despite their similarities - his older age and thus more developed moral code, having no one to avenge but himself when he believed himself worthless, his more privileged upbringing, and his relatively low drive to live. Alone, he would have died.
Then Kaz steps in. Kaz's role in all the crow's lives is that, intentionally or not, his ruthless rule of the Barrel creates a sort of haven that allows them to survive where they would have died had they stayed alone. Wylan is a really clear example of this, and though Kaz's intentions were at least partly self-serving, his involvement both kept Wylan from dying of exposure or street violence as well as prevented him from needing to do the more terrible things that it takes to survive in the Barrel. Throughout the books, we see Kaz kind of taking the brunt of enacting violence in Wylan's place - traumatizing Smeet's daughter, killing the clerk on the lighthouse. Wylan could get by making explosives in the workshop rather than having to shoot or stab or beat the life out of people. And at the end of the series, Kaz sees to it that he never will have to. Of course Wylan did bad stuff to survive when working with the Dregs, it's the Barrel. But the extent is greatly lessened because of Kaz's involvement.
Wylan's arc was never about becoming comfortable with violence, or becoming just like Kaz - the way people characterize him as some sort of ruthless murder mastermind is inaccurate and redundant with Kaz's character. He isn't nonchalant or celebratory about crime or death or violence by the end of the book. He doesn't HAVE to become like Kaz, because Kaz himself gave him the space to continue being decent, intentionally or otherwise. Understanding that dynamic is important to understanding what Wylan is like as a character and as a person. If you assume Wylan's trajectory is to become "Kaz 2.0", then you're going to mischaracterize him. I've seen posts about how Kaz was the Jordie that he didn't have to Wylan, and I think that makes a lot more sense. Because Kaz is willing to do the horrible things in his stead, Wylan has the third option otherwise impossible in the Barrel - maintaining his decency and surviving.
