The game text never defines "NPC." There's an implication througout, though, that NPCs are
characters with motive, feeling, and agenda. All of the moves and references to NPCs imply that. That would make
me less inclined to have it work on a mindless automaton.
The move requires that give an order based on your divine authority. What does that look like in play? If you're raising your voice with something like "In Bahamut's name, stop where you are!" then the recipient probably needs to understand your language (or at least your meaning and recognize Bahamut's name or holy symbol) for it to trigger the move.
Also... check out the Boons. Two of them play into this directly: a mark of divine authority and a voice that transcends language. If you've got that mark, any order you give could be based on your divine authority... even mindless undead could be affected. And a voice that transcends language? Well, now everyone (maybe every
thing) can understand you and your command. Move got a lot more powerful right there.
All that then interacts with the nature of the target in your game. Is a golem truly a mindless construct? Or a sentient elemental spirit bound by a wizard's magic? Or a new soul imbued into the construct by the Word of Creation carved into its forehead? Are zombies mindless corpses animated by some vile energy or virus? Or are they tormented souls with the vestage of their former lives? The answers there would impact whether you considered them "NPCs" or not, and what was required to invoke your divine authority against them.
It's fairly powerful--if it can affect anyone and any number of anyones, then it's kind of an unlimited defend move, with only the choice of redirecting the attack toward you. And since the paladin has heavier armor and better HP than many of her/his allies, and may want to defend innocent victims, it seems to have a lot of heft.
I don't want to take away part of what makes the Paladin cool, but I also don't want a situation where the paladin just turns on the attack magnet and suddenly none of the NPCs present have any options.
Yup. Pretty aswesome, especially if the paladin's on a quest with a boon that makes them invulnerable to the undead or something like that. Be a fan of the characters! There's plenty of ways they can still get in hot water.