I'll take 2nd strongest combatant over first mate any day. 2nd strongest combatant doesn't change whether luffy asks you to look after the crew or not.
These threads only serve as a dick measuring contest between the swordswallowers and shaftdeniers, 2nd strongest combatant will always be a better reflection of strength than a first mate status dictated by a situational occurrence. Fuck the intentions of your question, you know what you're aiming for when it reaches this community
First mate serves as a justification to someone's existence on a crew, 2nd strongest combatant is a direct reference to his strength relative to his crew.. that shit matters when we are talking about strength or trying to derive strength from a title typically given to the first member
I will always be happy zoro is a combatant and second strongest bc his feats reflect that, first mate wouldn't reflect zoro as much, he is a reliable defender not a great leader