She's also excluded from the iconic moments of Luffy being first recognized as Roger 2.0 in Loguetown whe he says goodbye to Zoro and Sanji thinking he will die with a smile on his face, or the TB moment when Zoro and Sanji try to sacrifice themselves for Luffy, or post time skip when only Zoro and Sanji witness Luffy's renewed vow to become the Pirate King in front of Rayleigh.
She's also not part of the Volume 100 Cover Page like Zoro and Sanji, and doesn't get to have the plot revolve around her story and her past in the two Yonko arcs post time skip like Zoro and Sanji.
Nami does have more panel time than them, and i agree she is the female main character, but that basically just means that she's more of an MC than any other female
She get's featured a lot sure. I think she even has more panels than Zoro and Sanji who were about equal or Sanji had a bit of an advantage in that regard, but i think that in many aspects she's pushed behind them, including her authority in the crew. Because i've seen people attempt to push her as "Luffy's Left Hand" with this trio argument, and we have Oda go out of his way to officially name Zoro and Sanji as Luffy's Wings/Hands.
It's kind of like Chopper having by far most panel time after the East Blue top 5. You can say he's the 6th main character and superior to all the other SH's in that regard, but to what does that amount really.