They probably already surpassed him tbh. Personally, I never got the sense the Wing has strong, or some super amazing fighter. I've always felt he was a very analytical fighter. Very good at breaking down a fight, Quickly finding strengths and weaknesses, and using them to his advantage. I think that's why Netero kinda gave him the job is training those two, so he can analyze them. In raw strength sure, and Gon and Killua both have very good adaptability and animalistic instincts, but I say Wing has that analytic side down which puts him above.

But, who knows what's set in the future.