You're aware that defensive ratings is literally measure of points scored per 100 possessions by the opposing team, right? Average offensive and defensive ratings per season are literally exactly the same because they're measuring the same thing - points scored per 100. You can just as easily say defensive ratings were high in the 70s because offense sucked.
You know what happens when I change your statmuse link to "best offensive ratings by decade"
best offensive rating NBA by decade
www.statmuse.com
LITERALLY THE SAME fukkING NUMBERS BECAUSE THEY'RE THE SAME THING.
The actual measure of defensive prowess is team-by-team defensive ratings relative to the league.
It's always so hilarious when y'all try to bring advanced stats into conversations while not even having a remedial understanding of how they work. Can't stand y'all old nikkas.