You do realize that McKenney actually opened up the FH defense playbook and in fact, installed new looks that past defensive guys never quite accomplished, right? He was not only given a HUGE amount of autonomy on calling the defense from the sideline, he was the on-field coach/leader as Appel was up top. I'm obviously not downplaying Appel's leadership and success, but if you "dont give [Coach McKenney] a lot of importance" in the defensive success FH has had over the past 11 years, then I'm not sure you are fully aware of how much influence he has had over the defensive cohesion on these teams. As someone else pointed out, the defensive players played as hard for John as they did for Todd. He had a great deal of ability over rallying the troops and squeezing more than 100% out of those kids when they needed it. The FH offense has thrown a couple wrinkles in here and there, but for the most part the offense hasn't changed much from year to year - but if you dont see the way McKenney revamped the defense, I'm not sure you watched the games with your eyes open. I think the last 5 titles FH has won, were made possible by a stifling defense that adapted better than many we've seen over the last 25 or more years.
I'm sure FH will stick with a lot of the schemes and plays McKenney put in place, but his presence (or lack thereof) will be hard to replace quickly. I'm sure the next coach will be more than capable, but they very well know they're stepping into some big shoes.