I don't think it's insulation vs him playing with a D partner that works for him. It's not any different than what the Pens or any other team tries to make a solid top pair or 2nd pair. Dumoulin and Letang worked great together for that same reason, they complimented each other's game. Marino had a style that really didn't compliment anyone we had because it was never the right fit and then the coaching was also dreadful, never really gave him or others currently on the roster and recently departed to other teams, a fair shot.
The biggest change is adding McGill from the VGK to coach that D properly and utilize their strengths with the right pairings - Something he did masterfully in VGK with what they had while he was there, especially early on when they were incredible with the transition game and working as a strong unit. Severson btw, severely underrated, 2yrs ago he was almost on the outs as he wasn't living up to that big 6yr deal, last season and this season his value is pretty damn high and the Devils adding Marino and Nemec insulates them in a smart way if they do decide to move on from Severson to add elsewhere and that add can be massive given the value Severson holds, his age, skillset, underrated defensive play while also being a solid 40+ Defenseman.
I mean I guess you will always fight your position on this and thats fine, but it's just not what it is.
Also their pairings are...
Siegenthaler - Hamilton
Graves - Marino
Smith - Severson
They rely heavily on Marino and Graves honestly is the right pairing for him, if we had kept Marino and had a LHD version of Rutta, he'd probably do well here even with Sullivan's idiocy in the way.