Grinch better be a goner once this season ends unless they become the 85 Bears the rest of the way somehow. As a UM guy you'll know better than most here how good Leonhard was at Wisconsin, and I'd be giving him a blank check to run this defense and hire his own staff outside of Nua. Need an actual defense instead of one that demands turnovers or will fail.
Coaching is certainly an issue with guys not knowing where to go and tackling, but their is also a talent issue that goes back to Clay that will need to be rectified.
I think Lincoln Reilly's philosophy is exactly what Baker Mayfield said it was, "to just outscore people", as someone else said in this thread his defenses for the most part have always been pretty poor. I think this is reflective in everything about his teams, you are right, there isn't a ton of talent, but there is also enough talent where you don't look like Vanderbilt or Northwestern on defense.
Grinch has certainly been handed the keys to the defenses at some blue blood programs (OSU, USC, OU) and I would say the results have certainly been pretty lacking. I do wonder if USC has issues evaluating defensive talent also, I look at one of our best players, Mason Graham who is playing at an All-American level as a soph, after being really good as a freshman. This is an OC kid who was a star football player and wrestler at Servite and immediately emerged as a difference maker for an elite team and USC barely recruited him. USC just can't let kids like that leave SoCal if they want to get back to being a contender. But that may get back to the lack of any kind of defensive culture/focusing to much attention on recruiting offensive weapons.
I am shocked that Leonard didn't get a job somewhere, my guess is he is going to hope to land a B10 HC job or an NFL DC job. I was surprised he didn't get the UW job, but I think they wanted to change a lot about their program and how they played. Leonard turned down a chance to be DC of the Packers to stay at UW and then was passed over for the fulltime HC job.