@Hattori I 100% get it, and I've argued similar points in the past and I don't think you're wrong. Oda probably misses more than he hits on handling depictions of sexuality and sex appeal appropriately, but I'm not about to go back over ever single scene that could conceivably be ranked as fanservice and give them a pass or fail rank to verify that gut feeling.
Not too long ago (and probably ongoing) there was a lot of back and forth in online tv and movie forums about sex scenes and if they should ever be done at all. A lot of people were of the opinion that they're not worth it because they 'don't move the plot forward.' There was a particular level of sexlessness that seemed to be argued for that I couldn't help forming a strong disagreement with. Sexuality is a big part of the human experience and a massive motivator for a whole lot of real-world adults, it would be weird to say it's the only thing we've got going on that's not okay to explore in art. (Not to say that's what I think you're doing, just why I have a bit to say and why some of it might feel mildly tangential).
And there's no easy answers here! Like okay, I've established that I think sexuality and sex appeal are okay as part of a story and can make worthwhile contributions to tone and characterisation even if they aren't vital plot components, but then do we judge Oda (and many, many other authors) not on having them, but for contributing to the overexposure of the specific kind of sex appeal that's aimed at straight men? Genre fatigue comes in a whole lot of forms. I go back and forth between sci fi and fantasy novels as I have my fill of the tropes of one or the other, box office figures are suggesting hard times for superhero story beats. Everyone, especially in mainstream manga, seems to target and depict the same sexuality in a lot of the same ways, so it's definitely reasonable to feel burned out on the boobs-in-your-face genre of fanservice too.
And unfortunately this male appeal overlaps with things that really shouldn't be sexual at all. Like basically anything involving exposed skin. If we look at Rebecca again, her chainmail bikini is something that has been abusively forced on her. I never felt compelled to look at her in that light because her situation is objectively awful (and she's a kid), but you can't escape the knowledge that divorced of its context it looks like fetish gear and that there's a portion of the audience who won't care about the context anyway. Because we know that nudity is such a huge appeal point to the demographic and that the kind of appeal is so common, we end up making it our first assumption that that is what the nudity is there for, at best in addition to symbolising vulnerability/freedom/obliviousness/pre-original-sin-ness or anything else the author might or might not have had in mind. Do we look at intention or effect in this case? How do we quantify the ratio of readers who 'got it' vs the ones who saw flesh and thought 'great, the author's saying put the book down and take a wank break' without digging deeper?
Then, is the answer to making these things feel less awkward equal opportunity objectification? But it's not as easy as that. Luffy, Zoro and Usopp show off most of their chests in their default outfits and have run around naked in baths, and Luffy flashed half of Amazon Lily, but it doesn't scan the same way. If you look at Q&As and polls on what women find sexy and what they look for physically in men, you find really different stuff from the inverse. 'Teasing in a skimpy outfit' is (broadly and generally) much further down lists of straight women's desires than for straight men. You see it fall behind things like hands and forearms, hair and beard grooming, the voice, and assorted personality traits. Things that have a much greater overlap with nonsexual character-building, so they pass through more subtly when they are done. This straight male kind of appeal that relies mainly on exposed bodies isn't just the most prominent way in terms of the number of people working on it, it also sticks out the most.
And you'll find different things again in what gay men generally look for in other men and what gay women generally look for in other women (or would want for fanservice targeted at them). That just makes it even more complicated and nuanced to find the most equal and equitable levels of sexualisation/objectification. And again do we look at intent or impact?
Getting that variety of fanservices aimed at different demographics would be great, but it would also likely only feel at its most natural and reach its target audience best if it comes from an author who is genuinely into it as well. (Although writing from the viewpoints of people who aren't you is obviously part of being a good author so experiments and attempts to capture the gaze of other genders/sexualities are admirable and encouraged!) There should be more female and queer authors writing what appeals to them, and it's a much broader cultural issue (in different forms across different parts of the world) that the industry favours the straight male version and markets anything else as a niche if at all.
I've just kinda settled on the point of authors should write what interests them and do it with all the passion they've got, and it should be on the industry to facilitate as many different kinds of people doing this as possible. Lots of things get written in lots of stories that don't directly add plot value - there are fanservice fights, there are fanservice character meetings, there are fanservice throwbacks to iconic moments. Lots of manga authors don't do cover pages the way Oda does, it's just the first normal page of the chapter with the title in between the panels. You could argue that when he's not doing a cover story he could use the front page to add more canon story instead of superfluous animal illustrations, but he does the animal illustrations because they appeal to him. I'm not going to hesitate to call fanservice out if it breaks my immersion in the world or characters to exist (again, the Egghead outfits and camera placement are awful) or if there are so many of these scenes the actual story comes at the expense of them, but I've gotten a bit past saying they outright shouldn't exist at all. And in that light, the statement that the character should be a willing participant in whatever scenario brings them into the spotlight rings true.