you're not wrong, but the strange thing is that Prude is in a position of power to do something like this, but hasn't. Either she's retarded or it's more complicated than that. In HxH power has to be earned, paid for, or balanced in some way, so perhaps it's less "killing" and more, as this page states, coming out victorious in a battle.
But admittedly I'm just trying to justify all this shit. Going off of the information we have, yeah, the ability kinda pokes a hole in the setting.