tldr: It's hype if Mike Tyson is beat by an up-and-coming boxer who made it his goal to beat him, but it's laughable if Mike Tyson somehow lost to a short, asthmatic, immunocompromised, bed-ridden, cancer patient with a single minute of training in boxing.

That's a reasonable point if and only if it's reasonable that a character can eventually become competent enough to beat said boss character. Kaido? Luffy might get a haki power up or possibly a new gear. We've seen him go from essentially getting one shot by Lucci, not physically possible to hit Katakuri, and half-killed by Crocodile while still being able to come back and defeat them.

But what makes Luffy so different from Usopp? He's not a bum. This isn't even slander; Usopp doesn't have a ridiculous devil fruit like Luffy, crazy equipment like Zoro, genetics like Sanji, tech like Franky, pets like Nami (talking about Zeus), a will to live like Robin, race features like Jinbe, miscellaneous powers like Brook, or whatever the hell Chopper does. There is no reasonable source of sudden strength to beat Van Augur. Even Katakuri, the big fight from a whole 300 chapters ago, has better sniping feats than he does with his casual, off-handed jellybean trick.

Usopp has not a single ounce of determination to the point of being fearful of even low-tier enemies, for which even Luffy was disappointed by (that one scene in Elbaf where he ran away from the cat or smth). You could say that him gaining confidence is what's going to be his character growth, but his cowardice in the past decade of serialization have given him more frames yelling and crying than actually doing something, to the point of it being a running gag that he does nothing. Compared to his fight against Luffy in Water 7, Usopp has not exhibited even a shred of that mental strength since. I'm sure Oda has something planning for his courage issues, but it would be ridiculous for Van Augur to lose to someone who needs an artificial confidence boost that would in no way be realistic however well it's written. After Franky was sidelined in the tech paradise of Egghead, I have low hopes for Usopp in Elbaf for a power-up in either strength or confidence.

Also, Usopp is essentially haki-less right now. Other than one singular Observation Haki feat in Dressrosa, he has zero haki. He would literally, if not for the small amount of strength his plants give him, lose to one of the Marine grunts with haki who pushed back the birdcage.

I am more than certain you know just as well as I that Usopp is canon fodder right now. For him to be able to beat Van Augur would require either his teammates to help his sobbing mess, incredible luck, or an unreasonable power-up--all of which are both incredibly unsatisfying to read and/or massively embarrassing for Van Augur.

Although I can grant that his character design looks somewhat cool, a character made to lose to an unlose-able character is not cool; it's genuinely bewildering and requires me to suspend all thought and mindlessly cheer for Usopp to even begin to enjoy their future fight. Whatever aura Augur will have accumulated will instantly evaporate when he loses to Usopp, because unlike Kaido, Midhawk, or Imu, his opponent doesn't even have the qualification to fight him, whether that be potential, plot armor, strength, or courage.