all coaches are different. styles, approach, motivation, hands on, age, background. the list goes on. Pettine started as an Offensive coach I believe Dom has always been D. This team could use a shot in the arm and its pretty clear Pettine brings a higher energy approach then DC. Ill take a younger firey guy right now over an older guy with a stale d. (im not knocking anyones age here) Jim Leonhard called him a hard ass. this team needs that IMO but yes its speculation on this.
Pettine may not have been a DC since 13 but that's not saying he hasn't been involved in coaching. (Clev and last yr working with the seahawks)
It isn't August but what we have is change from the same old mess we had. We have new coaches from all different backgrounds. Point being that is different to what with in house last year.