The bigger questions: How can Cullen not be bitter?
(...)
Cullen in a way as a child idolize The Order and for someone to come along and shatter that boyhood idolization into a million pieces, makes him furious. It’s a slow climb, a slow death. While Cullen is glad to not be a part of that downward spiral, he sometimes comes across as helpless as if he can do nothing about it. Thus I believe it adds to his anger.
I mean, I understand Cullen's story. I know what happened there. My criticism is not about his storyline, which is a very interesting one once you put it all together - it is specifically about the fact that we are never told this story. We have to put it together ourselves from scraps of information found in codexes, vague one-liners, unrelated conversations and third party references, headcanon the gaping holes left where the canon doesn't answer things, and come up with this awkwardly franken-story that each of us sees a different way, because we don't actually know.
I'm not necessarily against a change in direction for his character - I don't feel it was well done, though, and that leaves me lukewarm about his ever-changing characterization, and struggling to reconcile the various facets of his person into one cohesive shape.
The fact is, the pace of how Cullen feels towards the Templar Order is fine, nothing wrong with it. You just have to take a step back and understand why Cullen is bitter and there is a reason. A reason I cannot blame him for.
This, I cannot agree with, sorry. We should not have to take steps back and piece together a character's story for it to make sense. We don't have to do that with most other major characters in the series - their stories are told, not hinted at, and even when they change in radically different ways (like, say, between DAA!Anders and DA2!Anders), we are given stories behind those changes. What Cullen gets is:
Last few scenes in DA2: I believe in what the Templars stand for.
First few scenes in DAI: I don't believe in the Templars anymore.
Four years inbetween: [reasons???]
Cullen's story is not the problem. The lack of this story actually being told in narratively interesting ways is.
This is the same criticism I have towards Sebastian's storyline, for instance - if you piece together all the codex entries about him, all the things he says in dialogue and party banter, his backstory, and all the references that other characters make about him, Sebastian's story is fascinating and absolutely heartbreaking. But we're never actually told this story in a narratively interesting way, so most players have no idea that he even has such a good story to his character, and to them he's basically just that Chantry guy who whines a lot. Only people really really interested in him will go the extra mile to put his story together and see the whole piece of his character.
Cullen ends up being the same: we, Cullen fans, put a lot of time and effort into putting his story together and filling in the blanks and seeing the whole picture of his tragic character arc. Outside of our Cullen bubble, though, he's "that one Templar who was kinda evil but is a nice guy now I guess?" (actual words I heard the other day about him). We shouldn't have to walk three miles through the snow and up the hill to understand his character. People shouldn't look at him and say "he's alright I guess" - his story should have been told clearly enough that not just his most dedicated fans will understand it.
So it boils down to: Cullen's story is great, I'm not disputing that. I just wish we had actually been told all of it, instead of having to guess for ourselves.