It doesn't matter if Nami helping makes sense. in whatever way you think it does.
It contradicts stuff that happened before. "Don't interfere with another person fight." etc... Is Luffy a fucking hypocrite now?
If he can't stack it, Then he better go pack it.
He always got outside interferences though.
Against Arlong, Luffy was saved from drowning by villagers.
Against Loguetown Buggy, he was saved by (apparently Dragon's) thunder.
Against Loguetown Smoker, he was saved by Dragon.
Against Crocodile, he was saved by Robin.
Against Lucci, Usopp distracted Lucci so Luffy can recover.