I saw not much difference in 90s (post offside and backpass change) to most of the 00s, either in fitness or tactics, definitely not some huge jump. i'd say better quality pitches on average was more significant in comparing those two.the 70s/80s to 90s was bigger because of the impact of backpass and offside change alone. The 00s was a moribund time tactically that did little to move on from the 90s until Guardiola's possession/positional style took off. Things like the English league discovering 3 man midfields decades after other leagues were considered significant tactical "revolutions" worthy of hype during the early part of the '00s ffs.
Roughly speaking, i'd group the post-war stylistic era's into:
50s and 60s...though there's enough going on here in terms of tactical changes you could easily argue for both as standalone, but it's harder to assess if you're not ancient enough to be there first-hand, because of comparitive lack of footage available.
70s and 80s... variations of 3's and 2's for midfield and forward lines/4's and 5's for defence now dominant. Similar tactics, fitness, ruleset, pressing, multi-functional players become trendier. Often not good pitch quality.
90s and 00s until pep's barca...backpass ban and more lenient offside rule for attackers changes playstyles which then stay within similar tactical trends as previous decades, just becoming more refined. teams become more compact, fitness becomes more widely professional and analytic in many leagues, far better average quality of pitch in most decent leagues by the 00s. depth of competitiveness begins to erode post-bosman.
late 00s to present. Globalised tactical era begins spearheaded by Guardiola and Klopp's refinement of earlier concepts, out of which comes good pressing and possession as a new expected standard, rather than just as stylistic choice of some teams. Concept of multi-functional players in most positions is fully consolidated, though imo you can argue this happened at different times in different leagues throughout the decades. uniform high level of fitness leading to clearly faster games on average than 20th century stuff, stats/analytics era takes off. superteam/fewer amount of leagues dominance is fully consolidated. Sport fully devolves into corrupt capitalist excess.