As explained in the Yorknew Arc, there is too ways to gain power with Nen, either by naturally training it, like Killua has, or by sacrificing or putting conditions on yourself, like Kurapika using a condition to strengthen his chains. Since Gon was in rage of Kite, he essentially sacrifice pretty much his entire life in order to gain power that contested with the King. Not the smartest thing, however it makes sense in the world it was built in and at least it wasn't some bs THE POWER OF FRIENDSHIP, plus Gon was badass and his whole fight sent chills. Also when Killua realize there was what Gon did and how he couldn't save him.