Mushoku Tensei is objectively much worse than Made in Abyss when it comes to the “creepy” elements
Main reason why I believe this is that Rudeus behavior in Mushoku Tensei is never given any consequence or depicted in a way that the author shows that he is condemned for it. If anything he is rewarded in every way possible, he’s put into this new world and acts on these things with no hesitation or fear of repercussions because the author doesn’t even seem to have an issue with it. So pretty much it seems like Rudeus is a character people are able to relate to in those aspects and normalizes the issue.
For Made in Abyss it’s like the creepy stuff is snuck in I guess. It’s not like any of the characters are inherently creeps that the audience is able to relate to but the children characters being put in these specific small moments sometimes for humor shows doesn’t necessarily consume the entire plot of the anime. I still condemn it but it’s something thats able to be ignored while Rudeus’s behavior and backstory is apart of a huge part of the show and why he does certain things.
(I know “creepy” censors what I really mean but I was trying to keep my wording as light as possible)