Clemson allowed 7.4 explosive pass plays per 100 passes, which is top 20 bad. They allowed an explosive play on 4.4% of run plays, which is top 5 bad. Adjusting for schedule, they are sandwiched between Colorado and New Mexico. Those two powerhouses combined for four wins against FBS opposition (Texas State, New Mexico State, Hawaii and Washington State). Florida State and South Carolina were both top-level explosive offenses in 2012 while LSU was not.
This break-but-don't-bend approach to defense makes some sense for Clemson. If you have an explosive, up-tempo offense yourself, you want the other team's offense to get off the field in a hurry. The Tigers didn't force a ton of turnovers, but they were quite good on 3rd downs. That being said, Clemson was in the defensive dysfunction range in the number of big plays they allowed.
The offense was good, 9th in points per possession. They outplayed their peripherals, which were generally in the 10-20 range, by being very efficient the in red zone: 5.6 points per red zone possession, 5th best nationally. Tajh Boyd was obviously a big part of that success, and he finished 3rd in EPA+ (behind Manziel and Florence) and 8th in EPA+/pass. He was a healthy combination of efficiency - 67% completions - and explosion - 7th among quarterbacks. But he had a disappointingly large drop off on 3rd and long.
The good thing about having one major flaw is that one flaw is easier to address. And with Boyd back, the offense should be rolling along. But even if the defense had been able to keep more plays in front of them, Clemson was not uber-elite. The offense would still need to be top 3, not just top 10, to overcome defensive insufficiencies against the country's best. With Hopkins gone (the nation's leading receiver by EPA+), unless Boyd grows Manziel legs during the offseason, that probably won't happen.