This is a battle manga for 14 yrs old boys.
Indeed, and even fourteen years old can understand that, when some seconds are given the title of first mate while others aren't (even in data compilations like Vivre Cards), then maybe we should think that not all seconds are first mates.
But hey, maybe fourteen years old can answer questions like...
1) Why Vivre Cards only addressed a few number twos as first mates if they all are.
2) Why Rayleigh is both addressed as Roger's right hand man AND his first mate as introductory information directly from the author if those two are synonyms.
3) Why Oda stated every division commander shares the same rank if Marco literally holds a higher rank than them.
4) Why Sabo is in this color spread as the Revolutionary Army's chief of staff yet Teach's own chief of staff isn't here.
5) Why there's any debate at all about who will inherit the captaincy of the Big Mom Pirates if Katakuri is officially the first mate, and why Daifuku alludes to Katakuri's strength instead of his supposed rank as the one appointed to lead them in absence of their mother.
...And so on. Fourteen year old boys aren't dumb enough to not understand that not every crew is structured the same way and to not notice that, if people like Rayleigh and Beckman are explicitly referred as first mates while Marco, Katakuri, King, Zoro... aren't, then perhaps not every second man holds such rank.
(Which is the obvious scenario here).
I've seen you shitting on Zoro in the past, while simping for Sanji.
Bullshit. Not only I don't "simp for Sanji" (whatever that means in your twisted mind) but I've explicitly stated tons of times that I dislike the route Oda has been following with the character and that the cook has long not been of my liking, plus assuring in many other instances how obvious it is that he's weaker than Zoro, that he isn't Luffy's right hand man and so on.
Bepo is more than likely Law's strongest subordinate with direct portrayal as such when he beat with ease the right hand man of Law's novel main antagonist. And even if he wasn't, my point would stand because what I'm arguing is that not every right hand man holds the title of first mate, whether they are the strongest after their leader or not.
And yes, I admitted that Zoro is Luffy's right hand man because he is. But since Oda has made explicit distinctions between a right hand man and a first mate, I'm honest enough to not mix them.
!!STOP!!
Also, this Laffitte is chief of staff thing just came out of thin air one day and has stuck, the guy is just the navigator nothing more!
If Oda is using real-life for BB pirates crew structure then the first ship captain is just the helmsman of the 1st ship of the armada, the ship on which the admiral is stationed on, so the first ship captain has no real authority unlike the other ship captains.
Stop what? Understanding that we have no right to assume as first mates the many characters that have never, ever been confirmed as such just because people's beloved Zoro is Luffy's right wing and second strongest subordinate yet has combatant as his official rank?
If you don't like Laffite as Teach's chief of staff (ergo Sabo's equivalent in terms of authority rank) go complain to the same Vivre Cards stating so while giving the rank of first mate to a small number of right hand men. And I don't know what your first ship captain stuff comes from, but I'm not talking about it.