Yeah they are minimizing the losses in the secondary, which will be a problem when they're playing teams like Texas, Oregon, Ohio State, and USC.
JJ was an excellent game manager, you're right. However they're actually replacing all 5 starters on the OL, along with Corum who ate up a ton of carries, in addition to JJ and their top two WRs. Orji has a cannon but his accuracy is a major issue on the intermediate/deep balls. If his accuracy improves they'll be fine, but he has a ways to go, and his only weapon with any kind of production is Loveland the TE. Jayden Davis is supposed to be the future for them, so I think Orji has this season alone to prove himself, and I could see him being pulled if he doesn't get it together right away.
I'm big on SC over LSU also. LSU's defense as a whole was pitiful last year but they got bailed out by all the offensive weapons they had, and now they're gone. Also, people seem to forget, this is Brian Kelly. He's a solid coach, but that's been it for his whole career.