I think Rhule's love affair with NFL coaches may be waining.
You mentioned an emphasis on scheme (and I agree) but I also think part of the issue with guys used to coaching in the NFL is a natural tendency to take the psychological aspects of their players' game preparation for granted because they're used to working with mature, 30-year old adults. I'm not saying former NFL guys can't excel coaching at the college level but its got to be an adjustment.
In Bradden's case, he had high-level knowledge base, but he was taking over a young, unproven DL after Ty and Nash left a big hole. The pressure was on those guys immediately and Bradden was a first-timer when dealing with the stress, anxiety, and confidence level of his young troops. With the benefit of hindsight, we can be critical of Rhule for his hiring of both Bradden and Butler, given the make-up of the defensive team they were taking over. But it still comes down to stepping up to the plate and coaching.
FWIW, I will say, in Coach Rhule's defense, that he was quick to realize his mistakes (on both sides of the ball) and had been working to quickly correct them. I've been used to watching Husker coaches respond to perceived staffing mistakes by stubbornly doubling-down on the status quo.