That's a lot. The prison system is neither equipped nor designed to resocialize or rehabilitate people. He hasn't demonstrated any considerable change in his character or outlook on the value of human life that makes me believe he changed for the better.
He didn't make a mistake. He intentionally planned out the murder of his ex and how to hide the body and explain her disappearance and he did this to keep his children he neglected, which was the reason for her breaking up with him to begin with. And then he acted out that plan and stuck to it for months. Most people don't even commit to their gym memberships as long as he did to his cover story.
People aren't evil. But people also don't improve by rotting in prison. You can argue that means we need something better than prison and I would, but you can't argue that means he should be treated as redeemed or released early.
Dropping a feel-good out of context MLK quote to try and impress a future parole hearing is not a demonstration of character growth. Still referring to his victim as "my wife" when she had already broken up with him is not a demonstration of character growth. If he seeks redemption he needs to address those surviving his victim. If he wants to demonstrate rehabilitation he needs to do more than just get older and memorize meaningless platitudes.