I don't know if it was the same for you guys but the way Luffy became stronger was unexpected. You just thought he was going there to try to save robin just like he always manages to win his other fights. but when he came out and did that gear thing, it really was unexpected. Like in other mangas/anime you can always tell when characters are about to get stronger. They give you a heads up by showing you the character going through training or some other thing. but Luffy it was different.
I already know that Usopp is a smart dude so he will come up with a lot of gadgets and strategies to use them accordingly. Id Usopp,Nami and Chopper are on the same level, they are not really strong and they are not really weak.