I sort of had a similar conversation earlier. I think throughout the series the only edge Luffy has over Zoro is the emperors haki. I'd say they're all meant to cover a broad spectrum of things. I want to say Zoro is equal in raw strength as Luffy, but Luffy is more powerful/destructive and Zoro has more Endurance. They treated Zoro's 120 lb cannon the same as Luffy's cannon as they combined it, and then rounded the number up to sound better. In their fights they've been equal. As for the rest of the crew...One of the coolest scenes was when Sogeking was sniping people from on top of the tower, he's situationally awesome. And Robin's power is great but it's still limited by her physical strength, even though she can multiple it and gain leverage, i still don't think any of the monster trio could be 'crutched' by her. As in their so strong the could over power her limbs. I think Brook's power is awesome for the group, I think they want to make him more of a bard.