I suppose the issue I'm taking here is that "gender norms" are implicitly bad. That a woman should be made to feel like she's restricting her life and opportunities by taking on the role of the caregiver. I don't mean to imply that one should be confined to gender norms, but I don't necessarily think that breaking out of them is something objectively laudable. It's something, you can be normative or you can't, but to me it's a neutral choice.
I am not offended by a work of fiction being gender normative, nor do I think it has to negatively affect the functioning of its plot or world.
Well, generally speaking, I can agree with all that in the abstract.
However, I do think OP paints it's gender norms in a bad way. For one, the statement being discussed here, by definition, paints the motherfigure as a stiffler of potential progress that the character could be making by going on an adventure. That
is a bad thing and mothers shouldn't be viewed that way. Like, remember the Scott Lynch example I mentioned about a badass pirate mother? Well, she is still fulfilling the role of a mother, but she not only is not stiffling adventure, she's part of it, being involved in fights and being daring and so on. But another scene that is brought to mind is a recent one in My Hero Academia, where Midoriya's mother brings up her objections to his continuing to study to be a hero. She is conforming to gender expectations here too, but it's a sentiment that is thoroughly explored and treated seriously. And it's not depicted as stiffling, because she wants her son to grow, but given how injured he has become under All Might's study, she's worried that UA itself will stiffle his potential if he cripples himself, so she's not actually stiffling his potential but trying to ensure it grows.
That is a series that I think handled a normative gender role in a positive way. Furthermore, it didn't paint Midoriya's mother as the standard mothering technique. Bakugo's mother saw UA and thought "That was someone who truly sees my son". Those are mother figures who still nurture their kids, but in no way get in the way of their growth, yet do not act at all in the same way. And the statement OP makes places motherhood as a conceptual antithesis to growth into a man.
And besides that, it already confines women in hundreds of small ways, including how they are depicted in combat, which I've gone over many times how that renders them powerless when presented in a manga where combat is the ultimate deciding factor of all conflicts, or how they are constantly sexually objectified, etc. Maybe in certain stories, that doesn't matter much, but OP is more about escapism than perhaps anything else. It's possibly the most escapism driven work I've ever seen. I don't see how you can say that placing such limitations on a world that's designed around leaving the limitations of real life behind.
My thinking on this topic is born primarily from my own experience raising a now-six-month year old girl. My wife is experiencing a wide range of sensations that I am not, and given how wildly they swing and the intensity with which they burn it is evident that it is largely hormonal. Not to say that I am not a nurturing factor in my daughter's upbringing, but just that my wife is being driven far more strongly (and perhaps somewhat self-destructively).
She's doing the stay-at-home mom thing while I continue to work, which was a decision mutually agreed upon and in no way assumed or forced beforehand. But I feel sometimes like she is judged for not being in some way more independent or career-minded, as if the choice to raise the child is somehow lesser for conforming to gender normative ideas.
Well, that's fine and all, but on the flip side, I've known fathers (including my own) who was more nurturing and emotional figure than my mother was, I know other people's parents who were like this. We can trade anecdotal stories, but you can't just take your personal experience and then just assume that's how the world is at large. That's what science is for, and Evo Psych just doesn't have much to offer in that. Like I said, from my research, it's difficult to pin down, but what inherent gender differences there are tend to be minor and inconsequential.
On the social side of things, yeah, we're in a period of shifting societal norm, so as women become more accepted to be careerminded, the more people will think that's what women should be, which kicks off a set of new expectations. That's just kind of how things work in terms of culture, there is always a set of things your 'supposed' to be. That can suck or be awesome depending on how you fit into the cultural norms that society has set up for you. But in regards to how that relates to OP as a manga...
So to come back to what my initial point was, I have no problem with associating a mother with the idea of being nurturing, and I do not think mother vs adventure needs to imply something negative about mothers.
When you paint adventure as an indisputably force of good in your fictional world, and then paint motherhood as a stiffling force that you must escape to have your adventure, then that is an implicitly negative remark on what motherhood is. It's something to escape from, it's something that stiffles potential, something to resist once you are old enough to. Like I said, I'm sure it's well intended, but that plenty of men honestly, truly believed that a woman is happiest being a stay at home wife that raises the kids and cooks dinner didn't make it any less of a negative belief. Again, see waht I wrote in the first quote. In 800 chapters, motherhood is depicted shallowly, mostly taking care of kids until their old enough, then they go do whatever, usually because their too dead to do anything. I'm struggling to think of a scene that depicted anything more than how much mothers care about their children, rather than trying to help them choose their life goals/directions. Usopp's mother just stayed at home and was sick, Nami's mother protected them until she died, Robin's mother just told her how much she loved her and encouraged her to live, Ace's mother died by protecting him....Notice how none of them really have an active role in their kids lives, teaching them values or helping them strive toward their actual goals or anything.
I wouldn't mind if this was one or two, but this is more or less a consistent pattern from what I can see, and Oda saying quotes like painting motherhood under a brush like he did doesn't help. You can argue that a gender normative work isn't inherently bad. I can agree with that. But I do think that a work that encoruages gender norms for no clear reason and does it in a shallow manner so as to gloss over the negative implications of those norms, yeah, I do think that deserves to be criticized.
What about evolutionary Biology? If we're talking about hormones and such.
Tendencies in motherhood isn't a biological function, it's a social/psychological one. There is no hormone that makes you raise a kid a certain way, or even care about a kid. You can probably find evidence that many mothers find their kids doing something like talking for the first time indeed gives their brains a good ole seratonin blast, but that alone is too vague and broad to draw meaningful conclusions from. Lots of things give you brain a seratonin rush. If you have studies that talk about this, feel free to let me know and I'll go over them, but social norms are often used as to try to make sense of biological functions, but rarely are they anything close to comprehensive.