I'd say Usopp is the same as Blackbeard.
They scare easily, but they're not cowards, they're fearful. Bravery is not the absence of fear, it's what it is done in spite of it.
Cowards lack bravery and daring. I think Blackbeard needed both in heaps to betray the WBPs and do what he did. Similarly, Usopp may be last to run to danger, but he will run to danger.
Ultimately, I don't think Usopp shouldn't get it not because he fearful, but because what he wants out of life is pretty internal. He wants to be brave warrior of the sea, I think the joke of it is that he already is, he's just too discouraged to see it in himself.
Conquerors aren't all larger than life characters, but they tend to be unreasonable people, as I imagine a conqueror would have to be from the outset to believe in themselves and their aspirations.
I know not all of that applies to Chopper, who I think would be an interesting candidate for CoC, but I do think the little guy has some pretty bold and big aspirations in, essentially, conquering illness and disease or die trying, which he will if he practices medicine until his own death.
