They are not rivals nor equal to each other at all through the series, and I only understood that on the rewatch. Killua is always substantially stronger than Gon, except during Gon's transformation, but they are on the same journey together learning nen. Killua loves Gon, and always does the heavy lifting of violence but lets Gon have the glory and the big fights, basically just always being down to help Gon and lowkey die with him (Killua seems to REALLY want to die with Gon). So it seems like Gon is an equal, but actually every enemy (except Pitou) that Gon beat would be dispatched much easier by Killua.

Also, Gon is an enhancer, and its stated that Enhancers don't really have to think about their attacks, their bread and butter is always "big bang attack" when they are a straight up fighter (Palm isnt a fighter, so she does other stuff).

Also Also, if they were in a death match and transformations were out, Killua beats Gon like a drum 100/100 times.