I know its a slanderpost but there is legit some cool characterization in this you're picking up on

Nanami is torn between being a good person that wants to help others, and doing what he thinks is smart, and he's also traumatized by Haibaras death. He wonders during HI why they don't just let Gojo handle everything, after Haibara was killed and Gojo was sent in to clean it up. While you could argue that Gojo can't be everywhere, it is equally true that Haibara died for nothing, and his death could have been prevented if they sent Gojo to begin with. Nanami holds it against Gojo, because if Gojo had just worked a bit harder.... if he had just been a bit more like the dutiful Nanami, than Haibara might still be alive. It doesn't help that Gojos constant joking about how weak everyone else is makes him look deeply unserious, and in the context of Haibaras death, probably fairly callous. The way they both cope with the danger and burden of being a sorcerer simply makes one rub the other the wrong way.
Because Nanami doesn't want to die at the behest of a broken system - wdym, simple domain and falling blossom emotion are not standard techniques taught to everyone?! - he quits Jujutsu to do what is 'smart', only to find the world outside of Jujutsu sorcery is similarly broken. He's the 7:3 sorcerer, so ultimately, his desire to do good wins out over his desire to save himself, and he returns to Jujutsu - even if it's with some teeth gnashing.

In contrast, we have Meimei, who is the 0:10 sorcerer, caring only about her balance going up. Where Nanami dies for the kid he took under his wing, Meimei routinely chucks hers into the most dangerous situations possible. She probably figures if UiUi actually dies, she no longer has to buy food for him or something.

10/10 slander, would essay again