First Mate is a synonym for Vice Captain tho.
The best case that an Anti Zoro Pirate could make is that he's not the VC de iure because guys let's be real...we all know that he's the VC de facto
Exactly. The funny thing is that some people want to make as if First Mate means "first to join the crew".
While it's completely not like this. I mean, just take a fucking dictionary and you will see that First Mate means "the officer on a ship who is most important after the captain" "the officer second in command to the master of a merchant ship" .
Source -> Google lol
https://www.google.com/search?client=firefox-b-d&q=first+mate+meaning
If you search for "first officer", it literally sends you at "first mate", because it's the same thing.
https://dictionary.cambridge.org/it/dizionario/inglese/first-officer?topic=ship-s-officers
So there's nothing to argue, First Mate is the same as Vice Captain.
Being this a shonen manga, it also equates to being the widely recognized second strongest in the crew/group. Basically, the number two, which is what Oda showed us portraying the Number Twos of the main crews and groups on the color spread cover of chapter 1031.