@Riddler:
Isn't that kind of the opposite of the flashbacks message, though? That's the way Kuina's father saw the world, who, as we now know, was born and raised in the very old-fashioned and unprogressive Wano country. But the big dramatic scene of the flashback is Zoro telling Kuina that that is bullshit, that she is the strongest fighter he ever met and he's traning every day so that he will be able to beat her one day, and that when this day comes, he doesn't want to hear that he just won because of her gender/sex.
Saying that Zoro's flashback preaches that women are naturally inferior to men is like saying that Nami's flashback preaches that adopted family aren't really your family and only blood relation counts because that's what Nami says at some point in a heated argument with Bellmere. It's just completely missing the point.
Also, while there are obviously messages Oda wants to get across and sometimes lets his characters say out loud, we should always keep in mind that a character voicing an opinion doesn't automatically mean that he is vocalizing and mirroring the author's own opinion. I often see that happening with Sanji's character, i. e. he has a very antiquated view on women and treats them like dainty, delicate flowers in need of protection, so that means that Oda views women the same way, right? But none of the other main characters in the series seem to share these feelings about women, so why is Sanji specifically regarded as Oda's mouthpiece in this case? Simply because he is the one most vocal about his opinion?
That doesn't mean that you can't make assumptions about an author's values and worldview from his overall work or that Oda hasn't shown signs of sexism in the past, but we should be careful not to oversimplify things or make assumptions about him based on the opinions of singular characters.
I think with sanji it fells like oda doesn't have a problem with it, or else he would put sanji in scenarios where he would be forced to fight women or just suffer consequences of not fighting women, and not be like it's ok if you don't want to fight them, either they are good people down there(Viola) or you got nami and robin to save you.
With Kuina the problem is that male swordmen like zoro can tank absurd damage like back with kuma, or mihawk can cut mountains, but female swordman falls down the stairs and dies. Just imagine EoS, WSS mihawk dies falling down the stairs before zoro and shilliew get to him to challenge him for WSS title.