I believe it's not a misstep, but this is why I think Alex Garland has a big room for improvement as a director.
The core idea is whether journalists can always step out of the conflicts and just record things. But when the Jesse Plemons scene came out, we know these journalists has already been part of the wars. All four main characters have undergone changes:
Stephen Henderson, who had a direct confrontation with those soldiers (straying from the guideline Kirsten Dunst said), died at the end of the 2nd act.
Wagner Moura had been suffering from the psychological shock of Henderson's death (there was a shot that he roared), especially the fact he mentioned that Henderson probably died for nothing as western force is ready to storm DC. He was then somehow in the "what if" mode that Kirsten Dunst said no to Cailee Spaeny at the very beginning of the journey. So he didn't give a shit about anything except catching the president at the 3rd act.
Kirsten Dunst, who always said they should just press the shutter and go, got killed cuz she also broke the guideline for saving Cailee Spaeny. Just like her colleagues, she was unable to go back to the past after the Jesse Plemons scene and became more emotional and vulnerable.
Cailee Spaeny, who was like a baby or kid in terms of the press industry at most time, finished her journey as she captured the death of Kirsten Dunst. I think this scene might also reveal how Dunst established her own career -- based on a lie or something she couldn't really ask herself. That would also explain why she followed that guideline (couldn't face the ugly past). So through Dunst's death, Spaeny finally understood her icon, a real person beyond the wiki page, and also became her icon.