I see something similar. In the books, all the crew seem to be calm, reasonable adults, except Holden. That's not to say that other characters are devoid of emotion. They all have issues. Just that - in the books - Holden is the one crewmember who is close to losing it. And rightly so.

It feels like the opposite is true for the TV series. Everyone but Holden seems to be emotionally unhinged (i'm exaggerating here), while Holden feels like the calm, reasonable adult. Like others have mentioned, I tend to agree that Holden's struggle is internal and that's hard to convey on screen.

[the rest is spoiler](/s "

In the books, Holden seems to be the most affected by the Eros incident. He walked through hell and back with Miller trying to get out of that place. From that point, Holden and Miller loved and hated each other, depending on the moment. Those two were family from that point, because that was the only other person who had gone through what the other had. The other crew were, also, drastically affected by Eros, but for Holden and Miller the impact seemed to be more profound.

As if walking through Eros wasn't bad enough, then Miller died. That bond was gone. Afterward, he started picking up Miller's bad habits. Naomi mentions this time and again, that he's acting like a hothead or rashly, 'just like Miller'. He was a hothead before, like when he broadcast that the Cant was destroyed by Mars; but this was bigger. The universe just kept piling it up and Holden still had to be the captain. Then, to make matters worse, Miller starts showing up again and is only visible to Holden, making Holden think he's losing it. Still, he has to be the captain, and show a brave face. ")