You lack imagination, hence why the first time you mention is usopp "lacking the fire power" as if it was something we should even care about or something Oda can't solve easily because this is his universe and Usopp is a character who consistently showed to always have an ace up his sleeve.
We could have had mirages (perfect for a dumbass who attacks by charging with her head), we could have had Nami's "speaking for Usopp" turned into an actual misleading strategy, we could have had Page One finally tired of his annoying, abusive sister and faking to be controlled by Tama to "justify" treason against her (or simply making their relationship worse in our advantage), we could have had Usopp taking advantage on his own knowledge of the Clima Tact to set powerful traps in a tagteam or just making full usage of his arsenal, we could have had Nami controlling temperatures to affect Page One's spinosaurus' heat regulation (the spine), we could have had anything and yet we got nothing at all.
Who cares about levels, for real: Usopp's first fight out of his village was against Arlong's equivalent to Jack and Nami was able to take both Bonez's companion and Califa down. The problem here is Oda needing more sleep and lacking ideas for way too long.
We could have had mirages (perfect for a dumbass who attacks by charging with her head), we could have had Nami's "speaking for Usopp" turned into an actual misleading strategy, we could have had Page One finally tired of his annoying, abusive sister and faking to be controlled by Tama to "justify" treason against her (or simply making their relationship worse in our advantage), we could have had Usopp taking advantage on his own knowledge of the Clima Tact to set powerful traps in a tagteam or just making full usage of his arsenal, we could have had Nami controlling temperatures to affect Page One's spinosaurus' heat regulation (the spine), we could have had anything and yet we got nothing at all.
Who cares about levels, for real: Usopp's first fight out of his village was against Arlong's equivalent to Jack and Nami was able to take both Bonez's companion and Califa down. The problem here is Oda needing more sleep and lacking ideas for way too long.
Of course if that scene had not existed, Oda could have always come up with something new, he didn´t though and included that scene, and i am not going to argue completely disconnected from the manga, for better or worse.
Both are CoO users, as Oda had already pointed out, and pretty good ones considering they could tell Luffy is strong only based on their Haki, how is mirage going to work, we already saw with Sanji that invisibility vs CoO users is not useful. They are not fishmen fodder.
Speaking for Usopp would just camouflage Usopp´s attacks, and they would still have the same problem as mentioned above.
The majority of your solutions are pretty much from Kalifa, whether it´s mirage, their personality (Kalifa´s arrogance played a huge role) and so forth.
I don´t care about levels per se, especially since Usopp and Nami can´t be classically classified anyway since they have a very specific offensive arsenal. But not caring about levels does not mean not caring about coherency and consistency, and Oda not sacrificing them to justify certain match-ups. Even Robin and Franky fights could have been executed far better, for Nami and Usopp it would have been far worse.