Yeah I agree, there's no way a guy as analytical as Sweeney walked into this without doing a stack of research and convincing himself that the chances of Miller genuinely turning a corner and working out well for the organization are fairly high. Same goes for the rest of the management crew.
However there are still things that don't sit well with me. The Instagram message/apology just seems weak and a bone thrown to please the Bruins. On the point of atonement, well I'd argue if the victim and his family don't feel any sense of a genuine attempt on Miller's part to show direct contrition and regret for what he did, then you have to strongly feel that not enough has been done in that space and whatever exactly Miller now feels about his actions and desire to be better, he still hasn't stared the consequences and hurt properly in the face and addressed them. Then on top of that Sweeney has rather undersold what Miller did, and that's a pretty ugly thing to do, and they're paying Miller more than they have to, which just feels like rubbing it in.
Miller may very well have made a compelling case as to his change of heart and what he now plans to do to make amends and make a positive difference in the world and as a hockey player. But again, for me until he actually properly deals with the past, and until the Bruins are willing to deal with this completely honestly, then I'm not comfortable with this decision. As I've said, I'm not against this sort of thing in general, not at all, but I'm not sold on this particular case. There's a couple of very important steps missing that should have been completed/proven before the signing was made.