No one's played a major role in the fight against the god's knights. Being the weakest doesn't necessarily mean he was to be weak. Usopp already did something similar to Nami back in Alabasta, number 4 cracked Usopp's skull, he got back up told chopper there is a time when you cannot run and that's when your friend's dream is laughed at, and declared Luffy will become the king of the pirates.
