There is no way Kobe will ever defeat Luffy. Kobe is given this grand dream that he believes he will take down Luffy some day. He will never do that, even if he did ever reach that level of power.
Kobe's only purpose is to be the seed for good justice after the existing structure gets shattered. He will never fight Luffy. He may help fight the big end game bad guys, but he will not have that big of a role in that fight. And of course Luffy and Kobe will reunite in the end game. They started and have always been friends first, no matter what Kobe wants to think.
