Nami took out CP9 agent and those guys were all stronger than Water 7 Luffy, tho Ennies Lobby base Luffy is stronger than some of the CP9 agents due to an asspull power up.
They are called weakling trio because they are the weakest in Straw Hats.
They were never weak, they just had ridicously strong enemies. Now they all are incredibly strong themselves.
That doesn't mean she could have taken on Luffy like Usopp did. She used lightning...and we know what happens when someone tries to fight Luffy with Lightning xd
And the main reason why they were called weak wasn't really just because of their strength. That wouldn't be fair. What if every anime had a "weak group" just because they weren't the strongest? No, it was because they lacked the courage that everyone else had. So Usopp
was the weakest when it came to that however, he isn't the same as he was then, neither are Chopper and Nami. Though they are still the weakest among the crew, theres no point in calling them the "weak trio" anymore due to them not being weak anymore.
Thats the best part about character development. Usopp still freaks out when the crew is in danger and still overreacts, which is good because thats what makes him funny. But he hasn't shown any fear in battle. He showed confidence. Same goes for Chopper.
So Oda knows how to keep the fans happy. He improved their flaws, but still kept the personality.
