Holden isn't terrible, but the execution from the actor feels a bit stale/forced at times. Really, Holden's character feels a lot like Emily Blunt's in Sicario (Blunt is certainly better). The character, at least on screen, is definitely more a vessel for the audience to run through the story. Naomi is just, that actress is not good. You just never get the vibe that she is legitimately an engineer, let alone a badass one. It's night and day how insanely good Wes Chatham portrays Amos. That guy just nails the meathead war machine shtick, while very subtly exposing how badass of a technician he is, and how at peace he is with his spot in the world. Avasarala is interesting. It's clear she is so obviously over written, and is meant to be a walking "zinger". At times in season 4 it felt too much, but then she'll come back and nail it in a nonchalant way.
Amos, Miller, Ashford, and Murty just really kill it. It's kind of shocking how good those guys are. Murty was amazing this season. Perfectly cast.