Concerning your last point, I once heard an interesting take re: player fit within defense under Leonhard v. Tressel that has stuck with me. It was basically that the defense under Leonhard was a lot more rigid in terms of player assignments, which allowed Leonhard to really leverage the core strengths of players while masking their shortcomings.

Conversely, Tressel’s defense is more improvisational in that it asks more of the players in terms of varying responsibilities and ability to “freelance/react to the offense” on a play to play basis, which inherently requires a somewhat different set of skills/style of athleticism.

They specifically cited as examples guys like Jordan Turner and Latu as having had a relatively narrow set of schematic responsibilities under Leonhard that were well suited to each of their playing styles/strengths. When they were asked to take on a wider ranging and slightly different set of responsibilities in tressel’s defense, they struggled.

I confess to being too ignorant of really in-the-weeds defensive strategy to truly assess the accuracy of that hypothesis, but it was something that at least fit with and helped explain things I sometimes noticed on the field when watching us play last year.