i understand why people are upset about gojo's ending, but it definitely aligns to what gege planned for him as a character. not many people (if more than one: suguru) really cared about gojo satoru beyond the facet of being the strongest sorcerer alive, their main weapon, the six eyes.
from beginning to end, from birth to death, gojo satoru was made to serve jujutsu society.
you can count on one hand how many times the other characters are shown to really care about his mental, emotional and physical status beyond the fact that he can actually fight to protect them and the world. this is just how his relationship with others was. he was more an entity than anything else.
the few who got close (suguru and arguably sukuna) and tried to get close (shoko, yuji, yuta...) were still met with a barried he put between himself and other people, mostly because gojo himself recognized his role as the strongest, and to a point even enjoyed it. he didn't care for his family, had a few friends and wasn't even the typical mentor figure you usually see in anime. even the way megumi talks about the years they spent together is proof of that.
the people in this world mourning him as the strongest is something they need to do. but people mourning him as gojo satoru, the man, don't really exist in it anymore.
gojo only cultivated superficial relationships with every and anyone that came his way because he actually acknowledged his importance to the world. that doesn't mean, somewhere, somehow, deep within himself he didn't long for it. unfortunately, he didn't achieve that in his lifetime.
gojo wasn't written to be a happy character. he was written to show what the pinnacle of jujutsu society has to offer: tragedy, loneliness and war. however, that doesn't mean he was unfulfilled with it: he liked being the strongest, he liked fighting, he liked being gojo satoru.
people who cared about him, he acknowledged them. helping his students, his friends and colleagues. people who didn't, he dismissed. that's who he was.
so no. i don't think people "moving on" from his death is out of character. i think it's pretty much spot on to his character setting. he had his own version of a happy ending: dying in battle against his greatest enemy, meeting a loved one in the after life, and helping build a better society/world to the youth he fiercely fought to protect.
i think that, for him, in a sense, it was enough. for the fans... that's another story.