What really gets me is just how out of character it is for Luke to not want to redeem Jacen, because there have been numerous times throughout the EU where he has attempted to redeem darksiders who weren't his nephew. (Brakiss he tried to redeem 3 times for God's sake, Kueller, Kyp, etc.) Again, that mindwalker guy did say it was him changing the future that caused it all, so the in universe answers seems to be it's Jacen's fault for taking the actions that he did, and that if he hadn't that Centerpoint wouldn't have been destroyed. I think that blame can be passed around to many people with some being more responsible than others. Like Daala exiling Luke is specifically Jacen, and then Lumiya for having been...I guess the catalyst for his fall. IDK, depends on if you think he would've fallen regardless. The Mandalorians occupying the Temple however you can blame on Daala, Caedus, Lumiya, Boba Fett, etc.