I agree that the main issue will be that UM's D is a joke and has no depth. I do not recall any decent UM (10 wins) team much less an NC team with a D raked outside the top 15 or 20. UM has no such D.
BUT, I still have nightmares about how the O, which as you note pretty much returns intact, simply disappeared against any team with a top 30 defense. UM's "offense" laid an egg against KSU, was owned by ND and evaporated against FSU.
And we just hired a new and significantly less experienced OC.
So, can UM win this year? Sure, 9 games, maybe. But until the O shows up in a big game against a top flight defense, I'm not willing to assume that the D is the only issue.
Everyone is talking about 2014 and 2015, but why can't Miami win this year? They have an experienced quarterback with talent, one of the best running backs in the country, talented receivers, and pretty much their top seven or eight offensive linemen back. Defensively I have to think they will be better since they cannot be any worse; in fact I feel they will be much improved since the freshmen that were forced to play will now be sophomores. Jenkins, Crawford, Bush, Kirby, and Howard all have the potential to be all-conference. Granted, I do not think they will have a top ten defense, but top fifty or sixty is not out of the question. That should be enough to win the ACC. Florida State has to break in a new QB and V-Tech doesn't scare me. Additional, NC lost one of the conferences best players in Bernard. Clemson is probably the best on paper, but they lost key offensive players in Ellington, Hopkins and Freeman.