The biggest reason I push for Usopp having CoC is his entire character is in itself the adventure. His story for the past 1000 chapters leads to him awakening it at the end. Him dying a death of a Legend is what the story is revolving around. That’s who he is, he’s Usopp a Brave Warrior of the Sea. He will be known as such at the end. Characters like Zoro and Luffy were shown to be built different since a young age. They’ve been training, fighting for so long and have ambitions that surpass all others around them. Sanji possesses no such ambitions. Sanji from an early age did not show anything wild like say Law, Luffy, Or Zoro. Sanji simply continued working for Zeff.
Usopp on the other went on fake adventures with a crew he Captained. Everything Usopp does that’s Fake, eventually happens. This is a core part of his character.
Sanji exhibits nothing admirable like that. His kindness isn’t even something extraordinary. Nami is kinder then him. He was prepared to abandon the children in Punk Hazard until Nami said otherwise.