I am sure Butler has had some learnings over the past 10 years, but none of those learning occurred with him as the DC. As I referenced earlier, there is a huge difference between being a position coach and being the leader of the entire defensive staff. Rhule is taking a huge risk that Butler will excel as a DC when he really has no prior experience in that role outside of the bad 2013 year at PSU.
Regarding Leonhard, I don't believe many are saying he is the only option but rather a top option. Rhule even said he had many other P5 defensive coordinators reaching out to him. I simply do not understand why Rhule is not looking to bring in a more experienced DC so we can avoid on the job training. Again, this feels like a very safe and lazy choice and not a choice of Rhule pushing to bring in the best DC possible.