16 NPC's standing around?
Sounds like a bug, most of my story quests has had NPCs actively fighting, usually drawing the aggro for me so I can unload my heavy AOEs on the enemies.
If Retribution is the mission involving re-taking claw island, then I had a similar issue with NPC’s just standing around. But that was the only case, I’ve rather enjoyed every other mission.
Nothing changes if Nothing changes.