I mean if you want to use his evidence of remorse as an indication that he is redeemable, then there’s no good reason to omit Tyrion from that possibility too. I’m not even sure that Jaime’s crimes outweigh Cersei’s; Jaime is definitely responsible for Bran’s injury and has made threats against children, but Cersei ordered the murders of several of Robert’s bastards, who were all children.
All three of them have done terrible things, and it’s sort of… difficult? Strange? To establish a ranking system on who’s worse and why, as it feels like we’re assigning Bad Points based on the severity of the crime.
Where Cersei in particular differs than her brothers is that she is not regretful of most of the things she’s done. She is very focused on protecting herself and her title, and doesn’t care who stands in the way. You have to remember that out of all three, it’s Cersei who idolizes their father most and purposefully tries to make herself more like him. Her problem is that she is not as calculated as Tywin, not by a long shot.