If MR had big boobs, a curvier figure, and basically just had a body like Honoka, then no one would be giving her a hard time.
I kind of doubt that. If Marie didn't throw tantrums, fake cry, and hit every "child" mannerism trope,
then no one would be giving her a hard time. It's not just about being "underdeveloped".
And you can always count on me to give Honoka a hard time if it'll help. I say she also kind of acts like a child. And Tom Lee's "15-year-old schoolgirl" design comment from that interview way back also comes to mind. lol
I'm sorry but it isn't that serious.
The same could be said of you getting this bothered over sidebar comments. Marie was literally created to give off the air of a child. That's the whole point of being a (goth) loli. It's why Marie's DLC outfits were more conservative in comparison to start with. (See? This is on-topic. lol)
And we all know the pressure TN was under to make everyone (read: the girls in the game) at least 18 to avoid getting the banhammer again. That's why they
had to put MR's and Honoka's ages in their promotional trailers. If TN felt more unfettered, who knows how old MR and Honoka would be? It's not like every other Japanese company is super skittish about having characters less than 18 in their media while still putting them in "compromising" situations and attire. The "15-year-old schoolgirl" comment likely came from somewhere grounded as giving an age at all wasn't necessary for the character design example.
At any rate, it's all wink-wink-nudge-nudge stuff. No one is actually bleaching out their eyes. lol