Pfffffft. Defenses are soft these days. Typically, every year you only see two maybe three teams that play solid defense.
You go back, even just 15-20 years, defenses were much more physical, much more punishing. Yes, defensive schemes are more complex now, but thats because offensive schemes are more complex as well, not too mention new rules have been implemented that have greatly benefited the offense which allow them to score more points and stay on the field longer (ratings)....the game has evolved a bit, but you look at like the 85 bears defense for example and you tell me a modern defense can even compare to that. Nope, not even close to the same level.
Todays defenses have nothing on the defenses of old, besides a few exceptions. Teams were built entirely on defense back then, something you rarely see these days (bears, ravens and tampa bay are the only real exceptions but even then their defenses don't compare)