Eh, the "hard-ass" 1990s-2000s an enduring meme that I think could stand to be re-examined. When I re-watch clips and games from that era, my general sense is that defense overall was significantly softer, slower, and less physical than it is today. Overall, players then just weren't as skilled, big, athletic, or physical then as they are today.
I agree that cross-era comparison talk is fun but silly, which is why I like metrics like ELO which try to rate teams relative to their era.
The 90s and 2000s definitely had hard, physical defense, even if today the athletes are a bit better and the schemes are probably more refined. You can just look at the average ppg and the shooting percentages and see that it was more difficult to score. Any era before that, from the 80s on back, is really overrated when it comes to how tough the defense was. Yeah, you could get away with harder fouls and there were more fights, but often times teams didn't try that hard on defense unless it was crunch time and guys were playing a million minutes with less rest in between games. Again, you can look at the average ppg and see it was easier to score back then.
The thing about the Warriors is that during their first championship season, they really surprised a lot of teams with the amount of three point shots they were taking (and making) and how small they were willing to go. Teams were caught off-guard when Golden State would shoot a three pointer in transition instead of going in for a layup, or playing Draymond at center. Over the last five years, teams have adjusted to that style of play and mimicked it, so it isn't revolutionary anymore; all teams basically are shooting threes in transition and have small-ball lineups that prioritize spacing. Golden State's advantage over the last five years was almost as much stylistic as it was talent. Over time that style advantaged waned.
When comparing teams from other eras, they would be shocked to play Golden State. Depending on the matchup, it would be different; the 80s Celtics, 90s Bulls and 2000s Lakers often lived on contested mid-range jumpers, a shot that we have now learned isn't as efficient when you have three-point shooting. Could they get away with playing Draymond at center? Against the Bulls maybe, I don't think Bill Wennington could really take advantage of that matchup; but they probably couldn't against Shaq or Kareem.
I think a more interesting question would be if you put those classic teams in a time machine and had them fully comfortable playing the 2019 style of basketball. Curry takes 3x as many threes as Bird ever did, what if he shot as many threes as Curry, and there was more spacing for him to shoot? What if a solid mid-range guy like McHale developed a three point shot? Do we really think Jordan wouldn't have turned into a great 3 point shooter?