Luffy, Zoro and Sanji will remain the strongest fighters.
That doesn't mean Jinbe isn't a main fighter. He is, and Yamato will be too.
The rest of the crew will take on greater support roles, as they have already, but I am absolutely certain each of them will have to fight.
Usopp vs Von Auger is going to happen. Chopper is going to fight Doc Q (and probably awaken his DF in the process).
I'm less clear on who the others will fight, but they will fight. I hope Franky in particular gets a lot more shine. Brook was fantastic during WCI and I'd like to see more of his abilities, I don't doubt we will.