Davis is unquestionably a good coach.
UNC is a program that has always had problems sustaining anything above mediocrity.
While I think this is a big upgrade, I'm not ready to annoint them kings of the ACC just yet. Even if Va Tech and FSU stand still (meaning continue to decline,) Georgia Tech is currently on the rise, as are BC and Wake, even if it isn't sustainable in Demonland. Virginia and Maryland and NC State and Clemson will field good teams some years, and Miami will be back at some point.
It is a tough neighborhood to try and build a national power, even for a top tier coach, similar to what Holtz and Spurrier have tried to do at SC, or what Orgeron has to face at Ole Miss (of course, he is a tier in and of himself.)