Like the rest of the crew, Nami is a valuable member of the straw hats. She is one of the main voices of reason on several occasions and very often tries to knock sense into the boys for their everyday stupidity. How would she make as the captain which there is a difference from what she does and what Luffy does when he is captaining. She's often compared to a quatermaster but after looking up the role and what they do, she has little in common with them.
Where she is not the quartermaster and even more, why they only have one authority on board when it really matters.
Veto captains orders/counterbalance to the crew.
If this were a traditional crew, a quatermaster can forbid the captains orders. Most of her attempts to forbid or reject Luffy's orders almost never work since he never listens to her, even after taking a beating. When it all comes down to it Luffy makes the final call and the crew begrudgingly follow.
• She warned Luffy against an alliance with Law and he said no and went on to do it because he knew Law was a person he could trust.
• She argued that Usopp should stay after their argument and Luffy agreed with Zoro that he should face the consuqences.
• She wanted Zoro and Luffy to beat up Bellamy's gang for laughing at her and attacking Luffy. And Luffy ordered the opposite; to which is the only thing Zoro listened to.
Luffy definitely needs a counterbalance since a lot of his ideas are beyond stupid and the crew does a fine job of that.
A quatermaster is in charge of the supplies.
Nami is in charge of money and how to divide it. In general however, food and water is Sanji's turf. Franky is in charge of keeping the ship operational. Usopp on weapons management, and Chopper with the emergency supplies. She does not specalize in these categories so how would she know to get the right food for cooking up meals. What tools and supplies to get for weapons and boat maintnence and specifc supplies for the the medicine.
New members
Qutermasters are generally in charge of letting in new members. Well, as simple as it is. The crew usually have zero say in this. Of course they get their say but once Luffy sees a good person he wants in his crew, he refuses the refusal of them and his crew.
Asserting punishments
Let's just say, her punishments are for comedy purposes. I can't recall a time where she seriously punished a crew member. If anything, it's Zoro's style to do this, although I think Usopp is the only time a real punishment was set for a member.
Second in line if the captain dies
Nami doesn't legitmatly lead the straw hats. Yes, she sets rules, creates boundaries, and manages finances, and does a lot of the strategic planning. But, theres making the plan and then actually doing it. She makes the plan but she is not the one pushing it forward. Luffy is and more often than not he deviates from the plan and all the stawhats have no choice but to follow.
All in all, she has little in common with a quatermaster. Which makes sense because even in one piece, Luffy's crew is very different from a traditional pirate crew. But I won't deny she does a few QM roles such as: Navigation, strategic planning, and general structure of the crew.
The day to day orders are mostly figured out by the crew themselves, they know their role and they do it. Nami supplies the money which of course is essential to their survival. And she orders the crew as the navigator, which when you think about it, she's doing her job over leading. Let me explain, some don't like how she orders the crew on the ship but telling them to get the ship ready, where to go, and how to do it is the navigators job. Her personality just comes off as really strong and bossy so it puts a lot of people off.
The authority of the crew.
From the manga pov, Luffy is the only legit authority of the crew, and that's when it counts. Not a daily basis where he doesn't need to be authoritative. The dynamic will change when he is not present or avalible for communication. And that role usually goes to Zoro or Sanji with Nami doing it somtimes as well. Overall, once Luffy sets his mind to somthing without a good enough reason to change his mind, his word ends it.
Difference between Luffy and Nami is that she orders and makes the plans. Luffy is the official last word, and the one who carries out the plans in his own chaotic way. Personally, I don't see any captain characteristics in Nami. A voice of reason and a good second opinion, yes. She's the navigator in the ship.
During the times where it truly counts that Luffy needs to be a leader we see how much he outclasses her.
Luffy is highly emotionally intellegent. He can read a rooms atmosphere and make the correct judgments to help a friend or current enemy and easily change said enemies to be his friend or even ally. As Mihawk said, this is his greatest strength and as a captain, extreamly valuable.
He takes the fight against their enemies with confidence and strength of will. The way he inspires others is unmatched in one peice and it makes his allies all the more stronger. One of the best exsamples is in Wano when Luffy purposfully goes against Law's plan and breaks the Torii gate with a fantastic showing of power and resolve which not only ran the enemies out of there, but also inspired his allies to take courage and the time to defend their homeland was now.
If Nami were the captain instead:
There would be no grand fleet of insanly loyal members.
Enemies/rivals turned friends would have been less.
Territories claimed under the SH wouldn't have happened.
Every place the crew has freed was under Luffy's leadership and together, with his friends and allies, they make the world smile just a little brighter everyday. There's no other straw hat that could lead this kind love and loyalty to them. That's why Luffy is captain and his friends are his pillars that help him stand tall.
