Hmm... Well, there is of course a possibility that the other two royal guards aren't as big fighting monsters as Neferpitou. However, if even Netero doesn't want to face Neferpitou, I don't see how Gon & Killua could reach the needed level of power in a couple of weeks. Maybe if we had two Killuas who could devise a nefarious plan, but we have Gon who's too stupid for anything but direct face to face confrontations - and such confrontations happen to be Neferpitou's forte.