I'm not cocky, but they are going to have to kill me if they want to remain there. And that's not an easy task even for a god.

[Certainly he's not underestimating them, but he doubts that they are truly prepared to fight them as efficiently as they could. Chances are they are just mildly prepared or maybe just thinking that they are going to face normal pirates, not guys made of fire, guys who can heal themselves, and what not.]