Both made lot of efforts in their field, in what Luffy picked them for. Unlike most straw hats, they didn't have high skilled mentors and are actually self-taught. Usopp had nobody to teach him sharpshooting and tool bulding and Nami had to steal books to learn cartography and navigation by age 10.
Fighting wise, to be fair Luffy has broken genes, a devil fruit and had Garp training him since childhood. If these two were able to compete with new world fighters in fair fight without luck when they were literal east blue nobodies with little fighting experience 2 years ago because they did some push-ups people would complaint about powerlevels making no sense. They do try to stand up and fight back (Like Usopp trying to fight Sugar and Trebol, Nami refusing to obey Ulti at the threat of getting her head split open), they just don't have the level and unlike Luffy they dont have the ability to take 7372882 hits to improve their haki while being punching bag. Much easier to work the effort when you can afford to do that.
And they couldn't do a Koby either, he has Garp to train him, Nami had frail bookworm old men and Usopp some hakiless who and that's on Oda
