Each of the major Avengers (major here meaning headlining a movie) as well as several of the more minor ones, have their own type of story arc.
The Iron Man movies, and Tony’s parts in the Avengers Movies, have all, fundamentally been about Tony improving as a person. So, taking responsibility for the effects of his actions in Iron Man, sets him up to stagger through learning how to include and open up to people in Iron Man 2, and that, in turn provides the basis for the self-sacrifice he demonstrates in Avengers and then the more genuinely balanced teamwork he demonstrates in Iron Man 3. They kind of look cyclical, because Tony is a Mess and needs a lot more help than he generally gets, so that solving one problem typically just reveals the next onion-layer of dysfunction. But, overall, Tony improves as a person and emerges from each movie better than he started.
Thor’s movies are similar. In each movie Thor becomes a little less solipsistic, and a little more integrated as a member of his group and his community and takes more responsibility for himself and his actions.
Bruce Banner reaches increasing parity and comfort with the Hulk with each movie, his story is essentially personal. In Hulk he only develops the ability to control his transformations right at the end of the film, and notably, he does that after running away from New York, and Betty Ross, in Avengers we see him use that, and ends the film deciding to stay in New York and be accepted by Tony, instead of exiling himself. At the end of Ultron, even though he leaves again, he does so with Hulk actively making decisions, not just being let out as a last-ditch option.
Steve Rogers follows a cyclical arc, he’s constantly stuck circling back around and around the same conflicts. Even in First Avenger which is his origin story you have him dealing with the loss of Bucky twice (three times if you count him initially shipping out), and having to prove himself as useful twice, first as the little guy then as the chorus girl. Then during Avengers he once again has to prevent someone destroying New York using the tesseract, the exact thing he was doing when he was frozen at the end of First Avenger, although with a different enemy and team to work with. Then he fights Hydra and loses Bucky again in Winter Soldier. Age of Ultron then recapitulates Winter Soldier by forcing Cap to deal with internal betrayal by his allies, and fight Hydra, and Avengers by having him chase Loki’s sceptre.
Interestingly, Peggy follows an almost inverse path through Agent Carter. Although she’s not one of the core Marvel heroes, she’s an interesting point of comparison. She starts in essentially the same place Steve does in the final scenes of First Avenger, in a radically different setting, having lost the people closest to her, and having to prove herself, but spends the whole series gradually overcoming that and establishing new relationships and teammates and first regaining her old position, and then outstripping it.
One of the ways I think Civil War was very definitively a Captain America movie, rather than an Avengers movie, despite the big cast, or an Iron Man movie, although Tony is very prominent, is that it very much follows a Captain America arc, rather than an Iron Man one, or following the pattern of the previous Avengers ensemble films, where everyone is kind of following their own shape in tandem.
Cap is constantly being forced to relive old traumas, and in Civil War everyone gets sucked into his vortex.
Cap is losing Peggy… again. And losing Bucky… again. And having to fight the whole government… again. And having his team fragment… again.
Scott, who had somewhat established himself at the end of Ant-Man, is in jail… again.
Tony more or less loses every bit of progress he’s ever made, and is deal with being ‘the merchant of death’… again. Losing his parents… again. Having his relationship with Pepper fracture… again.
Bucky is being brainwashed and frozen… again.
Sam, who, despite his limited screen time, has consistently been a voice of optimism and an agent of progress is just up there to watch… again.
Wanda is being viewed as a monster and finds herself in the centre of a huge conspiracy courtesy of Hydra… again.
Natasha, who’s relationships with the group, especially with Steve and Clint have developed continuously through her prior appearances, ends up opposing them, and is having her loyalties questioned… again.
Even with Bruce Banner out of the picture Ross is making trouble because he’s treating superheroes like equipment, creating essentially the same conflict he created in The Hulk… again.
Clint is doing ‘one last job’… again.
Rhodey is introduced in Iron Man as a quintessentially secondary character, all his actions are directed towards fishing Tony out of trouble and cleaning up after him, but through Iron Man 2, where he’s largely a foil to Tony instead, and then Iron Man 3 and briefly in Ultron where he’s working towards an entirely independent, although related goal, he’s gradually become more, established as having his own story line. But in Civil War he’s back to pushing Tony’s agenda, and dealing with the fallout of Tony’s actions…. again.
We’re put in the position of questioning what Vision is and what he’s capable of… again.
And of course, Zemo’s whole revenge quest, which he carries out while listening to that last phone message from his wife over and over, is fundamentally an act of re-enacting the same trauma he experienced, repeatedly, on other people.
The only two exceptions are Peter and T’Challa.
Peter, since it’s his first appearance in the franchise doesn’t really have a previous trauma to go back to, although there’s a case to be made that resetting the Spiderman continuity by putting him in a fight full of older more experienced superheroes puts him back into his presumed prior role as ‘the little guy’.
T’Challa, is the only person who actively breaks out of the cyclical nature of the film. He begins the film seeking vengeance, for the death of his father (and, the Wakandans killed in Lagos, though not to the same deadly extent) but ultimately becomes the person to actively end the cycle of vengeful killing. T’Challa is the first person to vocalize the statement that Bucky is a victim, rather than a perpetrator. Even Steve, who has spent the movie defending him chooses to address Bucky’s role by saying that it wasn’t him, and that he wasn’t involved in Hydra’s use of the Winter Soldier. T’Challa also not only stops Zemo’s plan, but, by preventing Zemo’s suicide, he averts the death of the man who killed his father, actively giving up his own act of revenge.
Needless to say, I’m really excited for Black Panther.