@HeartOfDarkness:
Example of this would be nice.
Luffy punching Alvida helped Coby to develop more than anything else; the fight against Don Krieg showed Sanji what determination can really mean; Luffy destroying Nami's maps at Arlong Park was incredibly important for her to be truly free; defeating Wapol while protecting the flag of Hiluluk showed Chopper what a true pirate must be like; defeating Crocodile didn't really develop any character per se, but it was one of the most cathartic moments in the entire series in my opinion, as was defeating Enel or Doffy; Wiper allying with Luffy and co. in the fight against Enel was essential to his character; the Usopp moment in the fight against Lucci was one of the best for his development; also good for Usopp's character development was his short speech to the mooks during Luffy vs. Caesar. The Straw Hat crew fight against Sentoumaru, Kizaru and the Pacifistas was crucial for the story. And this is just a few moments.
I was more into your camp in the beginning of this discussion, but you're stretching your argument waaay too far. Is adventure the essence of One Piece? Yes, it's a story about adventuring in a series of islands in a huge sea. But the fights are some of the most satisfying and cathartic moments, both for the characters involved and for the readers. Are they the main focus? No, of course not. This manga is not about fighting, but it plays a crucial role in the climax of most arcs. And you just cannot deny that. The story cannot advance without most fights (especially those where Luffy is involved). It's no coincidence that the first chapter of the series, excluding the Shanks flashback, begins with Luffy sailing, then meeting a person that needs help, and finishes with him punching the villain who is tormenting said person; it's a prototype of almost all subsequent arcs.