I tend to agree that ILB isn't an overly important position in a 3-4 defense, but having great ILBs can be a gamechanger, especially ILBs with the skills that Jack possesses. He's the best LB prospect to come out since Kuechly and he's been a DPOY candidate pretty much from the get go. I completely believe that Jack can have that kind of impact.
Having Hill cover TEs is an option, but that stretches the secondary thinner. That means single high safety and we don't have a good single high safety.
Jack allows 2 high man while still having a dynamic coverage guy in the middle. If Mosley can improve which he still could, a huge weakness becomes a very big strength. Even if Mosley continues to stink in coverage, having a guy next to him that can take on the majority of coverage responsibilities makes a huge difference.
I think we can all agree that we need an upgrade at ILB next to Mosley. Daryl Smith showed his age last year, and he isn't getting any younger. Whether that answer is Jack or someone else, it needs to happen.