2 hits and he almost was out? Hisoka has more raw power and those 2 hits daged him badly.
As I said. Look at Hidan vs Shikamaru. Shikamaru would had lost in a 1 vs 1, so he had to do all kind of tricks to win.
With prep, a fodder like Shikamaru could defeat someone who defeated his sensei.
A fodder like Usopp can defeat someone stronger with a strategy. Strategy doesnt show you are stronger, it shows the difficulty to defeat your opponent so you use all your resources you have, in fact, you defeat your opponent first in your plans and mind and then proceed to fight and win in the real life.
So yeah, I would call it a high diff given the strategy, extreme diff would had been without the strategy.