Everyone else have a role in the crew but zoro. Luffy doesn't actually need zoro to become pirate king. He can be replaced with literary anyone. Free loader with no role among the crew
Most of zorotards thinks he is vice captain or right hand just to cover up his uselessness among the crew
When in reality there actually ain't any role for a vice in straw hats. All follow Luffy and acknowledges him as the one and only captain