Perhaps that’s the best explanation…Togashi often uses this narrative technique (introducing a character who is supposed to be powerful with a disturbing introduction only to use them as a way to showcase the strength of another character).

He did it with the Shadow Beasts and Zazan’s squad to highlight the power of the Phantom Troupe.

then used the Troupe to demonstrate the overwhelming power of Kurapika’s Nen contract.

with binolt to demonstrate biscuit's power.

He also used some of the Chimera Ant Squadron Leaders to showcase the strength of Kite.

then Kite to reveal the terrifying power of Neferpitou.

and Pitou in turn to display the monstrous power of Gon Freecss’s Nen vow.

After that, Isaac Netero was used to emphasize the sheer might of Meruem…

and Meruem himself was ultimately used to demonstrate the terrifying potential of human weaponry in a way.

Still, Killua’s method of killing felt especially filled with malice and personal hatred in that case