Seems steep for a filler encounter

"You said this was filler!"
"It is. I'm gonna filler ya full-a lead."

That is how it went in the show, despite being filler.

Filler != canon. Look at Samurai Champloo (though that may have been the mushrooms...)

This filler is actually canon. Oda wanted to do this exact scene, but he also wanted the crew on the grandline on chapter 100, so he cut it. but, Daddy Masterson is 100% GOda approved canon.

That's actually how a LOT of the 'filler' in OP is. It's all those little story blurbs that Oda put on the Chapter pages in the manga, and they got expanded and fleshed out to pad the runtime of the anime, so it wouldn't overrun the main story's pace.

Damn, they're really pushing this 'kill off Uousop' thing.

To the DM's out there; what would you do if one player was grossly underpowered? Would you let them respec or do something like this?

Hasn't really happened much in my group, but when we were in character creation for Hell's Rebels, our DM was very concerned about my character in particular not keeping up. I'd decided on a constable-archetype cavalier, and he's friends with more experienced players who didn't care for the class, so he was worried that it would harm my enjoyment of the campaign.

So we hemmed and hawed about it for a while, considering various alternatives and homebrew tweaks. In the end, I ended up keeping the constable as-is because it was the best fit for my character concept. Since then, we've gotten up to level 9 and I'm doing just fine with it, but I know that if there had been a need for it in the early game, he would have been willing to help me work something out to make the character fit better.

I'm generally fine with most players respeccing or changing to a new character as long as they don't do it every session.

However unlike those pansies I stick with a character until they die or win. Or the DM complains "they don't like my character" because he doesn't mesh with all her special snowflakes. If I'm not dying or struggling with my setup the DM clearly isn't trying hard enough.

When the GM give a trial to a player telling him "You do this, or your player is killed" very direct, right? Any story like that?

I don't really think Usopp's in any special situation. "You're relatively weak, evolve or die" is pretty much how we all reach level 20.

Man, if the GM threatens to kill the PLAYERS for failing a challenge, you're either crazy or at the wrong table. XD

Well, if the villain of the campaign is .... The Shadow....

GM sounds like Dark Bakura or Dark Yugi.

Eh, it may seem harsh but as DM says, he's able to have ussop walk away at anytime. He did royally fuck up the rest of the encounter and then ask for a do over to have his character come off the way he wanted, so giving him the option is pretty generous. Also if he wants ussop to appear brave, the risk of actual character death on his sense of honour is a nice touch.