It's very hard to see the logical explanation for players being better or football being played at a higher level back in the days.
Sports science leads to players running faster, running fast for longer, jumping higher, etc. Increased investments in statistics and analysis leads to players making better informed decisions and getting rid of low value actions (f.e. like long distance shots that you see less and less in modern football). The ever increasing wages for players, commissions for agents and the general value of the industry increasing leads to more and more competition for places in professional football both for players and for everyone else.
What can be put against that? In the past players came from poorer backgrounds so they had tougher character? The lower and mid level players had less money and therefore had more incentive to try and reach the very top? Performance enhancing drug monitoring was at a lower level?

Although some of it probably is true, this surely doesnt outweigh the arguments in the previous paragraph.
Football has changed and there definitely is room for discussion about style, taste and things like that, the more effective something becomes, the more sterile it is, NBA and the 3 point shooting is a direct example of that. But its very hard for me to see any basis for arguments like "the level of defending was higher back in the day" or "footballers were made with better stuff" or "the level of football was higher". If it was true, the money involved is so big that surely someone would've thought of setting up a football academy that trained players 90ties style and made a fortune for selling these superior athletes. Or maybe 70ties style, because I'm sure that people that grew up with those footballers also thought similarly about the 90ties and 00ties generation.