Its been harder to play defense in recent years, however, defense still wins championships. Specifically, playing better defense than your opponent and winning situations. Maybe the bar has moved in terms of how many points end up scored, and that changes the valuation of defense/offense numerically in terms of weighted value, sure...
but look at the list of superbowl winners and be sure to remind yourself Belicek is a defensive genius and a brilliant match-up designer.
The road to the top involves combining a great QB with a good line and good weapons, with a playmaking defense.