The main characters splitting up is one of my favourite parts about Hunter x Hunter. They all have their own goals and motivations so it makes sense. I feel with many other manga that the main characters stay together simply because they are main characters, and often some of them are used badly. It's a small thing, but it makes the characters feel more like real people.
And here we go, this is the first time in the manga that Gon defeats an opponent by being superior in strength. Volume 5, chapter 44. That's really late for being a battle manga, and I think partly what makes Hunter x Hunter much more interesting than most others.
It would be easy to then go overboard and have Gon and Killua be far stronger than everybody. But instead, already in this chapter we are introduced to another child character that seem to be very strong as well.