I never assumed that our defense would be as good or better under Rex - in fact, I had a feeling it would be like Gregg Williams dismantling a great defense to implement his own scheme, and failing miserably because the personnel didn't match the scheme. Sadly, I was right.
As for the offense under Dennison, it's hard to predict, since he wasn't the play-caller under Kubiak. But it looks like the offense he runs is pretty compatible with the BIlls' personnel.
http://www.buffalorumblings.com/2017/1/20/14331974/rick-dennison-buffalo-bills-offensive-coordinator-tyrod-taylor-all-22