One Piece Does Usopp Get Stronger. One Piece Manga and Anime Vol. One Piece prioritizes creativity in most of its action.
Giving CoC to Usopp who is still running from Page One would be like giving a smartphone to your 2 years old daughter. Where does Usopp appear in One Piece manga. The obvious conclusion of Usopps arc is him finally becoming a brave warrior of the sea like the giants of Elbaf and likely him achieving this lie and becoming a feared and powerful pirate captain.
Usopp could become a lot stronger with the power up of haki this is why I feel like his bounty should be raised.
Does usopp ever stop being a coward. To answer your question yes he gets much much braver. Led by the Fifth Emperor of the Sea Monkey D. No but he does become a god.