Is jail actually punishment?

Kind of a vent more than a question.
Please bare with me, it's a jumble in my head I just need to get it out around some supportive ladies.

My BIL is in jail. He did something that I would like to punch his lights out (repeatedly) for. I help his mum by taking her out to see him. I don't go in as I really don't want to see him. On the extremely odd occasion my MIL has no one else to go with her I will sit in the visit with her. To help her I remain civil and friendly.
She is in her 70's and has had an extremely difficult time coming to terms with what her son has done to his and our families. Affecting her health for a while there.
I am venting/writing because I am so annoyed at the criminal justice system (term used loosely).
Let me be clear, jail is a necessary thing. Some people need to be seperate from society for their behaviours, but herein lies the problem.
My BIL has slightly acknowledged his heinous acts but, after 10 months in jail he is now the same arrogant, game playing little turd he was before he went in. He has his mum wrapped around his finger because her baby needs support. (I think that people who have made highly destructive choices need assistace to help them correct thier behaviour) the problem is you cannot speak against him to her. He didn't acknowledge his acts, we heard one of them in court the day he was sentenced. He remains adamant it was only one despicable act (the act itself proving there was more)- the reaction from the victim tells me it was so dramatically much more. He has made excuses for it but not apologised and he sits there and tries carrying on like he is king of his little incarcerated fiefdom all the while saying how he will be able to get his kids to come and visit him . Mums got sole custody and, quite rightly, does not want the kids near him. We don't know what is going on with her as she has rejected anything to do with my BILs side of the family.
This leaves us with my older two children utterly ruined from losing cousins they grew with from birth.
The thing is. While in the slammer my BIL is blissfully unaware of the destruction, grief and pain he has caused to all of us from his disgusting, reprehensible and destructive choice.
So much for justice, he toddles on his merry way in jail while we sit out here trying to get our shit together and deal with destroyed families and relationships.
How is this a helpful thing. I kind of wish he had to sit there and watch the destruction and the families get back up without him and - something that would annoy him - he couldn't interfere or control anything.he actually has the audacity to tell me how to parent my children after he abused his.
I miss my nieces and nephew, would love to support the sister in law who hates my guts for some unknown reason, but he ruined that too.
Still can't see the justice.
Thanks for reading my brain fart and giving me a place to vent. Much appreciated.