Well from the perspective of on-lookers who think SHP have commanders and they are commanding the Grand Fleet something that actually never happens as Straw Hats don't even stay with grand fleet.
And Zoro seems to have even more authority than Luffy himself canceling Luffy's commands again and again.
But from that on-looker perspective, if we take Zoro as commander then Luffy has a commander stronger than himself.
From real world perspetive where we know SHP crew dynamics, Zoro is just stronger than Luffy period, commander or not.