what are you talking about? Luffy seems to hardly have gotten anywhere near his fighting potential yet. Luffy would already be gone without law? shenanigans I tell ya.
I actually think Zoro could kill Luffy mind you, he's definitely not as good defending against swordsman, but he probably has a whole nutha Gear or something he hasn't even brought out yet. Can't really measure Luffy or Zoro until they get back to bring-of-death moments really. Zoro needs another "progression" fight and Luffy needs for something/someone really important to him to be horribly mistreated with the perp laughing in his face.
As said I'm just evaluating what they have shown so far, difficult to take some hidden power bursts into account. Zoro hadn't been pushed to his limits by anyone post time skip whole Luffy had to put in already quite some work against his foes.
Samurai Arc will probably be Zoros Arc to be tested.