I strongly disagree with everyone who says that character arcs are unnecessary or that they are some newfangled modern convention that is only expected by people who have been spoiled by prestige serial television. This stuff has been part and parcel of men on a mission/WW2 action movies since the beginning. When you have a bunch of guys on a squad, each one has their own little story or motivation. One guy wants to kill this specific Nazi, another guy wants to get back home to help his parents on the farm, one guy has a thing for the war correspondent embedded in their unit, but she won't give him the time of day. One of the classic cliches is Eddie from company C, who shows the squad a picture of his best gal back home. Then when Eddie dies, the audience thinks, "Oh no, now he'll never get to meet his best gal again". It's overly telegraphed and has become something of a joke, but characters are supposed to have these little things about them that connect us to their story. This is especially essential in a war movie, where many characters will die and sacrifice themselves.
Even more importantly, the characters on the squad have a network of relationships. We know how Lee Marvin feels about Steve McQueen, how Ernest Borgnine feels about Charles Bronson, how Tom Sizemore feels about Adam Goldberg, etc. One guy on the squad is racist and is constantly badgering the one Jewish soldier. All the rest of the squad backs up the Jewish soldier and it's a bonding moment. Two characters are rivals but they eventually form a begrudging respect. One guy is loyal to the captain to a fault and the other soldiers resent him.
Rogue One has almost zero character relationships. There's no network that connects these people.
How does Bodhi feel about K-2? No idea.
How does K-2 feel about Chirrut? No idea.
How does Baze feel about Cassian? Other than some vague disappointment that Cassian was going to kill Jyn's dad, no idea.
How does Cassian feel about Bodhi? No idea.
How does Jyn feel about Baze? No idea.
How does Baze feel about Chirrut? They are friends and used to be guardians together. That's all we know. Almost literally nothing else.
How does Jyn feel about Chirrut? Other than the fact that Chirrut seems to respect Jyn for an entirely unknown reason, no idea.
It's easy to establish these things. It's not the special arena of prestige TV. Disney has shown that they are capable of this. One of the strengths of the Marvel films is that we get these little character moments where people interact in little ways. That was one of the reasons that the first Avengers was so great. That could have been done here so easily. I'm not asking for complex relationship dramas, just those little moments and small connections. I want to know how Baze feels about Bodhi or K-2. I want them to be connected in some way, even if it's extremely small, even if they only share a joke. There are only six main heroes here. It's a relatively small group. Even The Dirty Dozen, where we have the 12 main soldiers + Lee Marvin, Ernest Borgnine, Robert Ryan, and George Kennedy, manages to give us these character networks without a problem. It's a foundation to any war movie, and Rogue One entirely lacks it.