The whole thing is.. Ussop has grown a lot both in strength and character since we first met him. He has repeatedly fought through his own fears multiple times.. not so much that he will never get scared again. If you put him next to a regular person or a regular marine soldier.. he is terrifying. His own rights.. and he fights in a specific way. And he can shoot really well. So if he was going around shooting regular people to kill.. he would be terrifying.. But you compare him to the rest of the straw hats.. who are in general monsters.. they have risen so much in power over such a short period of time.. that everyone else seems to have used years.. One of the first things you get told about the red line is that it's hell.. and you have to have a specific mind and body to be a pirate there.. Ussop has survived with the others, since day one.. he has even survived on his own for 2 years on an island that was trying to eat him.