I would say this isn't true--and these critics bring up evidence that it's not true in order to argue that it is true by attaching a vague coda like, "It's not good enough/real/silly." Part of the problem is that a lot of people don't seem to have understood that Rogue One wasn't experimental just for expanding the Star Wars films to outside the main saga, it was also an attempt to make a film of a different genre within that same world. Rogue One was designed to be more of a war film, a team war film like The Dirty Dozen or Where Eagles Dare, a genre where arcs for the characters aren't necessarily present or aren't crucial to the story. Many of the amateurs making this criticism seem pretty young so maybe they don't remember a time when most movies weren't superhero movies. So to-day I've decided to compile a list of recommendations, in no particular order, of different films from a variety of genres that feature main characters with no "arc". Mind you, if the characters in Rogue One qualify as not having arcs, then many of the criteria present in Rogue One, such as death and decisions that don't jive with their previously established world views, would qualify a vast number of films for this list. But I'm going to limit myself to . . . oh, I put together a long list. Well, here's eight of them:
The Passion of Joan of Arc (La Passion de Jeanne d'Arc) (1928)
Most of the movie consists of close-ups on Renee Jeanne Falconetti as she gives her amazing performance of a woman who will not waver in her devotion while a panel of priests continually try to bully and manipulate her. So, ironically, Joan of Arc had no arc and she would've been less interesting if she'd had one.
Alice in Wonderland
This goes for just about any adaptation of Alice in Wonderland or Through the Looking Glass. Exceptions include some of the worst adaptations, like the Tim Burton movie. I love the 1951 version which does attempt to introduce an arc of sorts with one scene, the "Very Good Advice" song, where Alice seems to have learned a lesson about being too curious, but while the line about giving herself very good advice but seldom following is in the book as a narrative observation it's not something Alice realises about herself. In the best adaptations, like 1988's Neco z Alenky, Alice is the same adventurous and thoughtful girl at the end as she is at the beginning.
Seven Samurai (1954)
Some characters in this film, most notably Katsushiro, do have arcs but the characters most people remember best, Kikuchiyo and Kambei, don't have any arcs to speak of. Maybe Kambei's opinions about the villagers evolve a little but that accounts for a small portion of the film's four hour run-time. Seven Samurai inspired many other films, most famously The Magnificent Seven, and could be said to have kicked off the kind of morally murky action team war film genre, making it a spiritual ancestor of Rogue One. Of course, George Lucas was famously influenced by Kurosawa in making Star Wars, particularly by The Hidden Fortress, which is told from the point of view of two peasants. This is largely why Lucas tends to say Star Wars is told from the point of view of R2D2 and C3PO who, like those two peasants, have no arcs.
La Dolce Vita (1960)
Like Alice, the central character of this film, Marcello, has a series of strange encounters but remains basically unchanged by them at the end of the story. The film functions as a snapshot of a peculiar life and culture in fashionable Rome of the 60s.
The Good, the Bad, and the Ugly (1967)
Does Clint Eastwood's Blondie really change much over the course of not just this film but over the whole trilogy that began with A Fistful of Dollars? Does anyone? Maybe Tuco. But no, not really. Part of the fun is seeing how the world around these characters just can't seem to crack into their personal motives.
The Wicker Man (1973)
And I mean the original, thank you, I'm not about to defend the Nicolas Cage version. Sergeant Howie remains steadfast in his beliefs and motives throughout the film and so does everyone he meets.
Mad Max 2: The Road Warrior (1981)
After the first film, the Mad Max movies can be watched in any order because Max remains the same throughout them and the movies generally only reference the first one. Max is trying to get through the wilderness, is wary of people, he reluctantly helps out, and then he goes on his way.
Famously featuring one of the few pregnant characters in film history who doesn't end up having her baby at some point in the movie, we never even find out if the case Frances McDormand is working on is the wildest of her career. Like many of the films on this list, the story relies on her character remaining a constant as she reacts to the strange events in the story.
Some other examples:
Pandora's Box (1929)
Kind Hearts and Coronets (1949)
I Knew Her Well (1965)
Get Carter (1971)
Nosferatu: The Vampyre (1979)
Almost any James Bond movie.
Twitter Sonnet #949
A copy's plastered on the yellow glass.
The charcoal shades but shrug and seek for smokes.
Ornery mist was pressed in steel and gas.
The spinach hangs above the air it strokes.
Intensely dry cleaned coats descend through damp.
A shivered forest brain contains the fool.
A model made for brighter thoughts than lamp.
Engaged to sharks the stone was but a tool.
A handle made of bone reflects in spoons.
In kitchen walls a lattice knife grew hot.
Beneath the stairs, a larder darkly looms.
The dishes take some rust and missions rot.
Demands for arcs will run in circles fast.
Forgetful droids and young neglect the past.