I'll have to disagree on some of that. Could be wrong, but...
First, I don't consider the tempo to be a temporary gimmick to get us into the win column. But more importantly, I think this defense has to have been designed from the day of Banks' hiring to be uniquely fitted to be the counterpart to our fast tempo offense. And if so, it follows that we are recruiting players that fit that unique defensive philosophy.
Change the offense, though, and you'll immediately have a defense that's mismatched in philosophy and personnel.
As for the offense evolving... Nico will be our first QB in this system to have the benefit of learning from an older QB who already knows the system. IIRC, Milton had only a few months in the system ahead of Hooker (or was it visa-versa?), so they were learning together directly from the coaches.
So maybe in his third year Nico might be ready to incorporate more of what Heupel's offense is capable of. But I don't see this offense "evolving" until defenses start showing they can stop it--with something other than supreme talent at each position, ala Georgia.