Oh?
A first mate:
"A First Mate is the top officer on board a ship after the captain. Mostly, they may fill a number of roles from checking stock to making sure everyone else is doing their job on the ship. They answer only to one person on a ship, the captain." - Pretty sure Zoro submits to other crew mates. The way the Strawhats operate give everyone equal status, with Luffy as the only nail standing out needing to be hammered down.
"Essentially, the first mate is the one officer the captain must put full trust in and pick carefully. They are the captain's right-hand man and if the captain is not at hand on the ship or is otherwise incapacitated, the first mate is the next in line to take over the captain's job."
So basically you think Zoro does this? Even though the only time he did was on Thriller Bark when Kuma arrived. There are plenty more instances in which Nami and Sanji perform the strategising and ordering of others. These two take charge, Zoro simply sleeps in the corner doing **** all. That's what he's meant to do, it's a part of his character.
He's widely regarded by those who don't know the crew well as the first mate, this is probably the only evidence you can come up with, right? Well he was also named as the "true captain" on Whiskey Peak. Does this make him captain too? Nope. People who don't understand aren't worth listening to.
