And what development did Usopp have in those arcs?
Not chickening out in a fight? That he did already at Arlong Park, or Alabasta, or Skypiea.
The only development we might count is his 2º personality, Sogeking, which is not really a development, but more like a gag/"mode"/"powerup" (temporal stuff).
And the first three chapters of postts Usopp didn't show development, aside from his new physique. He "lied" and you the reader believed him. And his lie was convincing because he took care of some fodders. Once we're back on track and have actual great threats, Usopp was the same like always.
It's like saying that he has development because if he returns at this moment at his village, he would be a reliable warrior strong enough to defend his land from any threat in East Blue. But that's not true, he simply would be a big fish in a small pond. His "development" is only strength wise. If instead of Kuro pirates, the ones who invaded his island would have been a bunch of kids, he would have been able to defend it by himself at that time.