That's valid I think.

Other characters have actually made decisions to show they've changed. Touka's decision about Yoriko's execution maybe harsh but it's rooted in her ideals that a parent shouldn't abandon their family (like her dad did). Saiko and Urie have gone from passively letting things happen because they want a family (eg. Not calling out Mutsuki). Now, they're willing to fight for what the think is right.

Suzuya might not feel any guilt for killing humans or ghouls even now but atleast he's become mature and responsible as far as taking care of his squad and underlings go.

Tsukiyama, Ayato, Hinami, Akira etc, all the characters have grown and changed in some regard and it shows in their actions. So it's a fair thing to say about Kaneki.

But I think in Kaneki's defense, he's been bombarded with one shitty thing after the other. Just in :re, Shirazu dies, Arima dies, Kaneki regains his will to live...just to find out he's dying.

Characters like Mutsuki, Kaneki etc have repeatedly faced different kinds of trauma that they're just broken in many ways.