The offense is definitely better. Tyrod Taylor is much better than any of us thought he would be.
The defense is definitely worse. Don't forget Aaron and Kyle Williams have been out most of the season. That is a big loss. Plus, I think the LB's over-achieved last year too.
Team disciple is definitely worse. It's reflected in a ridiculous amount of penalties . Marrone ran a tight, Ryan a loose one.
Bottum line is Rex has had more talent on offense and less on defense due to injury. The schedule looks favorable to make the playoffs but the Bills are just an average team folks.