This excuse has been brought up many times before, and I simply do not buy it.
You're telling me that WSJ is going to take the most commercially and criticially successful manga of all time out of their selection because Oda wants to do some unconventional storytelling (something that could be ascribed to a lot of OP)? The manga that brings them in millions a year like clockwork. No. It's hard to believe that Oda is held on any level to the same standards a typical mangaka is, but even doing that to a typically successful mangaka is insane. There's no way Oda doesn't have Carte Blanche to do whatever he wants,. Or, even if he somehow doesn't, lets think this through for a minute. WSJ kicks him out of their selection. So what? What is the worst that could happen here, seriously? He takes his stupidly successful manga and completes it in another magazine? Who in all the fuck is going to reject One Piece?
No. Whatever reason Oda does what he does, it's hard to believe it's under editorial mandate. Not to say that Oda doesn't listen to his editors if they advise him, but you're suggesting Oda's not doing this because he isn't allowed and he is forced to do otherwise, and I just don't buy that.
Furthermore, what proof do we have of this? I don't mean "Well, Look at how even Toriyama wanted to do the androids, but one call from his editor and..." No, that just means he trusted his editor enough to follow his advice, especially since he was his former editor not his current one. You're going on the assumption that Oda wants to depict these things, but is blocked by the heads of WSJ, and you're not the only one. Several people seem to take this as gospel truth. And I want tangible evidence of this, like an interview with Oda saying such, not just speculation.
And besides, I'm not saying 'show explicit sexual content', I'm saying 'show characters interested in relationships'.
No, you misunderstand. When I say their teenagers, what I mean is they're awkward and have no idea what the fuck their doing. They kind of pussyfoot around and uncertain how to deal with their feelings. Mineta is depraved about it and turns people off of it, while there are a few others that go along with his antics to a lesser degree, but most show they are affected by women's bodies but try to be respectful about it like Todoroki, or just the idea that they can get somewhat close to women like when Sugar bakes cake and women pick him as the favorite. It's light stuff, somewhat like OP in that regard, but then when it comes to acting on genuine feelings, few people do anything not because they lack interest, but they are uncertain how to go about it. Ochako and Deku have no idea how to act toward one another besides being friends. They're attracted to each other, and like each other, but are not sure how to express those feelings and are even conflicted about even having them. That's being a teenager.
Sanji is a teenager age wise, but doesn't have this problem (nor does anyone else in the manga). He's not shy and he has no confusion about the feelings he has toward women, and expresses these feelings without restraint at any given opportunity. So, when he encounters mermaids who are equally open and upfront about being into him, the fact that he and them don't really do anything, that he just sits there drooling, that's not a normal human reaction. You get someone that eager and willing and you get women who are also eager and willing, that usually goes somewhere. And for the record, I'm not saying that I want anything explicit shown. Obviously. It's a kids manga and the last thing I ever want to see is Sanji's nude body thrusting and making an o face. But you can work with implications or even just outright saying "Sanji's over there making out with the mermaids" without actually showing it.
And when you put Sanji aside, the fact that their teenagers makes the way the characters act more jarring. Like, sometimes it's acknowledged that what Nami is wearing is provocative as hell, but most of the time, it's flat out ignored. Lets say that Luffy is just straight up asexual. Okay, but Usopp has been shown to have an attraction to women/nami. But nearly every guy thinks Nami's (and most women's, since it's hardly only Nami dressing like this) outfit is barely worth a second glance most of the time. I'm not saying everyone should act like a pervert degenerate or something, but teenage boys tend to be highly distracted by attractive women wearing very little. Hell, men in general tend to be highly distracted by attractive women wearing very little. But no one seems to actually want to get into a relationship with Nami and Nami doesn't seem to want to get in a relationship with anyone else, and her suit doesn't really offer any tactical advantage, so she's just wearing this outfit that barely shows off any skin around men who acknowledge she's ridiculously gorgeous but don't have any interest in actually doing anything with her, be that relational or sexual.
For me, that's pretty thin. But even if we take this perspective on the event, this does not meet the standard that MHA set. I said the fanservice is at it's best/most acceptable when it's character based. You're arguing that it's gag based, and objectifying Nami and Robin's bodies and basically making them look like complete idiots or creeps for the sake of a gag is not good storytelling for me.
I'm pretty sure I said something similar on here when that chapter was released too. Gags that work with the characters they depict enhance the story, but if they have to break character/world rules to do it, then there's cohesion lost, and that's just not worth it for a joke.