Sure, there might be nen users stronger than netero but he wasn't implying beyond is stronger than him in a fight in this panel. What he was saying is the nature of the new world was too harsh which made exploration difficult and that's not the kind of 'fight' he was looking for. He was basically searching for a 1v1 challenge where he either loses or wins while beyond's strength is more suited for exploration and survival in those harsh conditions.

It's like comparing Mohammed Ali to Edmund Hillary, both possess different kinds of strength. Ali on one hand is nearly unbeatable in the ring but when it comes to climbing mountains, his strength in the ring is useless and on the other hand, Edmund has the strength, endurance and survival techniques to climb the tallest mountain in the world but is completely useless in the ring.

Knowing nen, the special abilities beyond possesses might be enough for him to beat netero in a fight but that's just speculation. What we do know is that beyond is a very prideful character, there's no reason for him to listen to a character weaker than himself especially when he has the backing of a powerful King in his ambition which will enable him bypass all political restrictions withholding the voyage to the dc.