"In there prime" may be a bit of an overstatement. But that wasn't the issue going into 2008. The offensive line had gotten old and it all fell apart from there. The defense hasn't been considered really good since the Tuna was Head Coach back around 2004 or 2005. And even then, it was over-achieving more than it was talented.
For me, this year hinges on Lee and Smith. If Lee can stay healthy and Smith can return to his Notre Dame playing days form, then this defense as a collective could be really good. Lee and Smith's play will inspire the younguns to work like they do, study like they do, and play with their all like they do. That is, of course, assuming the offense can return to something resembling their 2016 form. I've addressed in other threads my concerns about replacing Free and Leary, but if they have viable replacements, and the aforementioned happens regarding Lee and Smith, then the sky truly is the limit for what this team can collectively accomplish.