Agreed about Luffy here.
I just wish there are some character-exploration moments in which Zoro or Law fighting against strong enemies, while side-glancing from afar at Luffy playing around and running away from enemies chasing him, and understands Luffy so much that they say to their enemies, "That brat wearing a strawhat...may never escape being a boyish child who get scolded and slapped by us and being extremely dumb most of the time."
And then Zoro or Law slice their enemies while looking cool and all before saying,
"...But never forget. That is solely because you, are not worthy of HIS WRATH, that defeated The World's Strongest Living Being !!!"
Moments like this