I think people gotta stop taking it as x protagonist is on the "level" of x villain before they fight.
As we've seen with many other fights in this series, characters tend to ascend in strength mid fight or bring a new power up not seen prior.
Right now the question is if Franky can surpass someone like Sasaki. I fully expect Sasaki to absolutely demolish Franky, but only at first. This was my expectation of Ulti/Nami/Usopp as well (though not nearly as bad or quick), and even that I half expect 1 or both of them to still take her out later on.
The main drive of these characters is to see how they can surpass their opponents by being the underdog. Whether you thought it was "plot bs" or not, Luffy vs. Katakuri was the perfect example of this.
This is how I see every calamity fight coming or even Luffy/Supernovas vs. Kaido