Yeah, but there's still a depth allowed to them through what you find out. EVERY. TIME. You speak to Sera, you get something new, a whole new direction for her character to take. Each conversation is the start of a new character path, that proceeds to go no where, because the next time you talk to her, she's on to the next one. It's not that they build on each other and offer new insights, they are literally a character moment that exists almost exclusively in that particular moment you're talking to her, and then are gone the next time you do so.
Varric, Vivienne, and Josephine have new layers exposed to show previous actions in a new light - Varric introduces us to Bianca and focuses on Hawke, basically being the player avatar for how we (well, I) feel about Hawke. Josephine's quest ends with her expanding on her past and why she is devoted to peaceful resolutions, furthering the contrast of her and Leliana. Even Vivienne, who is probably the second least developed main character in the game after Sera, has that moment with Bastien when you give her the heart of the snowy wyvern where you see for a moment that she is more than the Iron Lady, that much of her attitude is about projecting an image.
Sera, in turn, gets none of that. Or, rather, she gets contradictory versions of that - she's about the little people, no, she's about sticking it to the nobles, she wants to get the world back to normal, no she's just out for whatever fun she can get. She gets these contradictions built into her character with no concern about how they fit. I don't mind characters who are hypocritical, who hold conflicting beliefs. But the fact that when you get the ONE opportunity in the game to call her on it, she shuts you down, and the conversation never comes up again... That's horrible character work, because it's not exposing facets of a character. It's saying 'this character is a hypocrite and has no intentions or inclination to be anything else.'
I'd argue that these aren't necessarily contradictions, in that a character can believe in helping the little people while at the same time being selfish and wanting have revenge against nobility because of a bad relationship with her mother. Characters can possess moral dissonance where they can genuinely want to do to a good thing and yet can't help themselves in doing another or perhaps having another motive that isn't exactly selfless.
Sera's motives are ultimately not straightforward in the least and are wrapped up in personal issues that the narrative doesn't present clearly because it's Sera giving you her backstory and desires, a person who doesn't have the maturity to explain what she wants in an easily understood manner. Take the rooftop scene, which I think does at least present Sera's actions and beliefs in a new light, the whole thing feels ridiculous and out of no where and its supposed to. Sera talks about her relationship with her mother and how she feels betrayed by her lie and why she wants to create new memories to replace the bad old one's. But she doesn't directly tell you that event was the catalyst for her negative attitudes elf culture and the nobility, and neither she she tell you that having friends is an another word for having family in her mind. Probably because she doesn't realize that herself. You have to decipher that out for yourself, which is problematic when the narrative doesn't provide a psychology textbook to help you along. It is frustrating and annoying when compare it to say Cassandra's or Cullen's character arcs. That said, I have to wonder if the Dragon Age writers did it if only to do something different, as kind of experiment. Inquisition has over twelve characters and all them going through the same structure of character development arc of Hints of Backstory/Sidequest/Important Player Choice/Emotional Revelation/Final Friendship Speech would be somewhat tepid so they decided to do something new with a character they call the "Wildcard" in their promotional materiel.
Look at this way, Sera gets angry when you attempt to criticize her methods in Verichel. She greatly disapproves. Two years later in Trespasser if you didn't criticize her methods or still managed to be friends with her, she decides to improve how Red Jennies function. Sera gets angry when you don't agree that the Dalish worship demons. She greatly disapproves. Two years later in Trespasser she gets emotionally tired of bringing up her issues with the elven culture and religion and decides to be at least tolerant and actually be sensitive about the impact that new revelations about your faith can have on a person.
Why is such esoteric character development being used here beside Bioware having the need to do something weird?
Maybe because it was showing that most people don't always react well when dealing with something they just experienced? I think that describes Sera quite well. After almost every main quest in the story, "In Your Heart Shall Burn", "Wicked Eyes and Wicked Hearts", "Here Lies the Abyss" and "What Pride Had Wrought", Sera is consistently either angry, frustrated or deflective. In some those occurrences you can try to talk to her about it, but most of time she's deflective or wants to focus on something else. She spends most of time actively avoiding things that bother her and the one of few things she does talk about it likely took years before she could anyone about and even then she told you about it so she could essentially forget it and replace those memories. She's a perfect example of a person using avoidance behavior to deal with anxiety issues. Of course, she eventually is able to express herself and really move past her issues somewhat but like I said it takes years, which is why it took two years after Inquisition to finally understand the need to use actual tactics in her Red Jenny operations and to be tolerant of elven culture. She's slow and frankly kind of stupid, quite young and has bad coping mechanisms.
So yeah, it takes time her to actually grow up and develop, time that is unfortunately offscreen that is justifiably annoying, but if I were to be honest having a character didn't rely on the Super Important Only Two Options Player Choice (Iron Bull, Cullen, Leliana and Cole) or the Let Me Listen To Your Self-Doubts To Make You Better Forever (Dorian, Cassandra, Varric, Josephine and sort of Sera) for their character development and instead decides to play the long game is a welcome if disorienting change of pace. Fact is Sera is a young twenty-something that probably wouldn't have all her major emotional issues mostly solved by talking to the Inquisitor during a big adventure that directly picks at side issues. That shite takes an exhausting amount of time. Trust me.
That said, I get having all that growth happen in Trespasser feels somehow cheap and undeserved, but I for one appreciate that Sera was one of the few companions in Trespasser that used to the timeskip to develop on her own. Character growth is still a thing even if it comes at the very end, right.
(f*ck this is long)