As of now, the dubious honor of "weakest defending champion" in the CFP Playoff era belongs unanimously to FSU, who came into 2014 riding high from an amazingly dominant season and then proceeded to look like crap all year right until Oregon smacked their program into irrelevance in the Rose Bowl. 2015 Ohio State, meanwhile, was one of the most talented teams (in terms of future NFL prospects) in history, and all of the defending Bama and Clemson teams have been incredibly strong. 

I think, though, with the losses of some of their best defensive players, their generational QB, and their offensive mastermind, LSU may well be an even weaker defending champ than FSU was. I certainly don't see Steve Emsinger developing Myles Brennan into anything close to Joe Burrow.