[TooPurePureBoy]

Sure it's a big world. From what we've been shown though (no mentioning of details in later arcs of the manga) there are plenty of nen users in the world, but the number who actually train in all the basics is actually pretty low. I have a feeling that most of the people in togashi's world that use nen in some way are doing it with little to no knowledge that they are actually using an energy called nen. People like the "Spiders" and the Zoldyck Family for instance; fully trained nen masters who have no affiliation with the Hunter Org. are extremely rare.

I get the feeling that the number of people outside the Hunter Org. that actually know that nen exists is like way less than 1% of Togashi's world population.

Whether they fall in the top 100 or 200 or whatever (I find no joy in arguing semantics) my point is that after training with Bisky, Gon and Killua are really high up in the ranks of your average nen user. The very small percent of actual masters are really the only ones that are above them. The problem is that they are REALLY far above them. In order to bridge that gap they need actual life and death battle experience (though if I were in charge or raising them I'd probably argue they are a little young for that still). No amount of practice will bring them closer to people like Hisoka for example.