Before y'all miss the point, were the male and female characters designed the way the were for everyone's enjoyment or for a single demographic's?

A single demographic, clearly.

My wife listens to books on tape basically all the time, and some of those books are pretty horny and treat the character designs of their men in words the same way that One Piece treats the character designs of women in pictures. As such, it seems to me that those particular books are also targeted at a single demographic; and while I don't think this has actually been studied by anyone that I'm aware of, it seems at least anecdotally that there's more current written fiction geared exclusively towards straight women than there is geared exclusively towards straight men.

My point here isn't "waddabout books, those are bad too"; it's to point out that the existence of media that's geared toward the enjoyment of some demographic or another is perfectly okay. One Piece doesn't need to be aimed equally toward every demographic. Anyone who wants to like it is allowed to like it. If someone doesn't like it because of the character designs, that's fine too; the authors of the series aren't obligated to alter their character designs to appeal to everyone. They can make it however they want.

This goes doubly for the random art that people post on reddit that r/mendrawingwomen frequently links to. Artists aren't obligated to appeal to everyone equally. First and foremost, they're trying to make something that appeals to them. And if people are positioned in a way that some people find attractive and other people find awkward-looking, if that's the intent of the art, then that's fine.

Now, you bring up kids, and I want to say that I think the idea of educating people about the difference between fantasy and reality is important, and that's how we need to be dealing with misconceptions coming from things like porn. r/mendrawingwomen is not the kind of subreddit that's ideal for doing the kind of non-judgmental education that needs to be done, though.