The 2017 offensive and defensive rankings of the Pittsburgh Steelers' opponents is not an accurate barometer of how 2018 will play out — but it's a starting point to gauge future success based on past performances.
Generally speaking, there are not vast turnovers on NFL rosters, nor additions of players via free agency, or via the NFL draft, that can make enough of a splash to single-handedly raise a team from the depths of the cellar to the top of the charts.
On the flip-side (my favorite side), there are players who may be purged, retire or depart for greener pastures — developments which may impact a team's future success.