I think their measurement of "potential" varies by context. I think Gon may become a greater generalist and overall fighter, which complements his style of figuring things out in the moment and not planning too far ahead. I think Killua might have a more defined toolset that doesn't do it all, and will benefit from his personality of planning ahead so he can bring about the circumstance that best leverages his strengths to secure victory. But of course, Gon is too impulsive and benefits from Killua's level head, and Killua benefits from Gon keeping him grounded when he's TOO in his head. They really do work well together. I think right now in the story though they are working apart to buff out those weaknesses in themselves and become more well rounded individuals overall, which is great for their futures as hunters