Yeah, but unlike DBZ (or Bleach, the other DBZ) the characters all power up... Luffy is strong, but I still don't know whether Luffy or Zoro is stronger. The rest of the crew is also becoming stronger than I ever imaged they would, too. Even Usopp, who I thought WAS worthless "grunt fodder" until the Enies Lobby arc.
Look at where Bleach is at right now, though... The main characters leveled up a bit, but no one even had the slightest hint of a potential to reach Ichigo's level.
In OP, everybody is staying with their same different in levels, but they're leveling up together.
IMO, Luffy and Zoro are about the same level, with Sanji slightly trailing behind. As far as sheer battle power, such as in a one on one battle, we're yet to see the full potential of Franky, Brook, and even Robin, but they're clearly strong to the point of being close to the highest three's levels. (Robin's abilities seem to waver though... Sometimes she's seem as being monstrously strong, while other times she can barely defend herself, and chooses really weak, ineffective battle moods in lieu of her powerful attacks). And before anyone argues "THEY'VE HAD ONE ON ONE BATTLES," I mean they haven't had as many as the other characters.
Usopp and Nami trail in last, but they ARE getting stronger, even if they seemed to be the most normal characters of the crew.
Chopper... I don't know where I'd put him. He's definitely a lot stronger than Nami and Usopp. I'd probably stick him somewhere above Robin but below Brook and Franky. I'm not considering "monster Chopper" in this equation because a fighting technique in which he has no control isn't useful.
From when they had Vivi... Holy shit, did her fighting level fail hard. I always wondered how she got to be Miss Wednesday.