Well it seems you really need some one to walk you through step by step, you should really see the movie again also just in case but,
Steve- He has a significant arc in TWS. First of all at the start he's trying his hand at the whole spy game with SHIELD, traditionally he's more of a soldier and he even states this but he still tries his hand at it, trying fit in with the modern world, by the end of the movie he's feed up with the spy-trade and his role is that of the soldier, no deception in his line of work. It's not his core character. That's something he discovers conclusively in this film. Also at the start perhaps his most pivotal arc is the one with Bucky. Maybe it helps if you're more familiar with the comics and just how much he's haunted by his perceived failure with Bucky's "death" in the war. There's decades worth of buildup in the comics but there's enough in the film, i.e the Smithsonian stuff and flashbacks, the whole end of the line stuff that is payed off in the end. Then there's the general kinda depressed mode that he's in at the start with whole man out of time stuff, focusing on just the missions, as the film progresses Steve seems to get more open to Widow's attempts to hook him up with a date with Steve learning Sharon's name at the end. At the end after his confrontation with Bucky which is the culmination of that arc,the whole guilt ridden/haunted Steve to one who now not only knows Bucky is alive, but maybe there's a real chance to save him. At the end of the TWS Cap has a clear mission purpose going forward. I daresay he seems cautiously optimistic after being so uncertain of if he still had a role in the new world. That's very significant character arc movement for Steve.
Natasha- she was a former KGB agent who essentially believed she had reformed by joining SHIELD. It's revealed that she's essentially a cipher, she has no real set identity, or even real sense of who she is anymore aside from her whole Black Widow persona, she is what the mission needs/dictates her to be. the whole secret/mysterious aspects of her character is very intentional and part of what she is as a covert agent. When she discovers that she has become nothing more or perhaps was just a tool who's morality is only as good at the intentions of those who wield her, and the revelation HYDRA SHIELD, force her to seriously reexamine everything about who and what she is and what she stand's for. At the end with the destruction of SHIELD and the fact that she uploads all her own personal secrets along with that of SHIELD, we have essentially seen the death of the "Black Widow" as we know her. At the end she's essentially a blank slate, starting over which direction she'll go remains to be seen. If that's not a significant character arc than there really is no point trying to explain anymore but I will...
Bucky- Granted he's somewhat underused/ more low key in the plot although is very pivotal to Steve's arc and his own. The saying less is more applies here and Winter Soldier was very effective in the film. He's basically Bucky who at the start of this story is believed dead. Now we learn that not only is he alive but he's been used as an assassin by the very organization that Steve now works for and also partly inspired it's initial creation. there's the revelation that they've tried to destroy who Bucky was and turn him into just a mindless drone assassin, a tool, a blunt instrument perhaps the extreme end of the costs to mind and soul that the business entails with Steve, Cap, Nat, Fury, and Pierce all also suffer from and deal with the consequence of to one extent to another. At the end we learn that the villains were not entirely successful and that perhaps their is something in there to salvage and at the very end we get a big hint that just maybe he's starting to become aware of just who he is. And this is a guy who was "dead" at the end of the last movie. If that Resurrection Arc is not in and of itself a "significant arc" than I give up.
Well let's not forget Pierce- We are introduced to guy as friend of Nick Fury who wants favors with Iron Man, will move heaven and earth to bring his friends killers to justice, only to have it slowly revealed that he's a man who's been totally consumed by that world of lies and deception to point that he really sees no difference between good or bad, he's just interested in the bottomline, power, although he probably sees himself as some kind of savior. The betrayal and revelation of that are somewhat significant and a symptom of the overall troubles facing the characters. This guy falls a long ways from Iron man at birthday parties to Hail Hydra with his dying breath. I think the fact that he started the story alive to end up dead also counts as significant development for his arc.
And of course we seem to agree on Fury lol. Either way I think you should watch the movie again.
