This is a good question. Unfortunately, the NCAA uses statistics like total defense and scoring defense to determine their rankings. That would be fine if everyone played the same teams. Miami has to play in the ACC, home to some of the nation's top offenses. Meanwhile teams in the SEC or Big 10 don't see the number of high powered offenses on a week in week out basis. I think the true measure of a defense should be the amount of yards/points you hold an opponent to under it's average. If you hold a team that's averaging 35 ppg to 20, it's more impressive than holding a team that averages 17 ppg to 10. At least that's the way that makes the most sense to me. If you consider that Miami held high scoring offenses FSU, UNC, Pitt and WVU far under their averages, you could make a point that Miami had a top ten defense in 2016.
Just for $hits and grins, I ran through a few sets of stats and the numbers are favorable to Miami's defense.
The per game scoring average by Miami's 12 FBS opponents (I excluded FAMU) was 30.17
Against Miami the average was only 19.83. That's holding opponents to over ten points below their average.
Only one team scored more against Miami than their season scoring average and that was Virginia Tech who averaged 35 ppg but dropped 37 on an injury depleted Hurricanes defense.
Notable performances: FSU (avg 35.1 held to 20) UNC (avg 32.3 held to 20) Pitt (avg 40.9 held to 28) NCSU (avg 27.0 held to 13) WVU (avg 31.2 held to 14)
Edit: I'll throw in App State (avg 29.2 held to 10)