I went back and read the manga, and this manga does something different from others. Rather than introducing new villains and simply telling us they're many times stronger than the last ones (a la DBZ), they just introduce various villains of different strengths at the same time. Plus the way the nen system works, it's not about power levels and aura all the time. It's about who gets caught off guard by not knowing the other's ability. You fukk up and don't put up a guard fast enough, you are finished. IMO, Kite is about as strong as the bomb devils.
No one you've seen is as strong as anyone in the phantom troupe though. Those nikkas and the Zoldycks are the most powerful we've seen so far. The ants are kind of a plot device to help bring Gon and Killua (who are still very weak) up closer to the beast level. For those of you still thinking the ants are overpowered, I'll give a slight spoiler and say that there are Hunters (and others) out there fully capable of dealing w/these dudes rather easily, they just haven't been introduced yet. This is a Loooong arc.