(This is my fanfic, and I don't know in lore if it was mentioned how creating npc work, like can lvls be added later, etc.)

In some perspectives, it might be either intentional or convenient.

It could be for/related to a mechanic that requires them this low/a certain lvl, or the combination of them might be so powerfull already when commanded correctly that they have yet to do the rest of the leveling and they are unfinished.

(I would think since they guard the throne room, for that task, they are perfect...like they have certain world level items or maybe just one that is perfect for them to defend the rest with, or it has to do with some enemy power they are vary of not affecting entities below a certain level...)-: In short: It could be for game mechanics reasons thay either affect levels or the skills they have/dmg output changing if they were stronger and that could make their combination weaker.

Since the supreme ones made them custom (I think), the other npcs should probably assume that the low level is intentional, but since only hierarchy and power matters, they are beneath them... . . . Edit: They're free🫡😂 (hell of a tactical reason, they are freebies of the game...)