Don't know if those guys from the past having travelled in a time machine would actually live up to their legendary hype in modern game.
So much has changed, the referring is far more critical of tackles, you simply can't get away with some of the Gentile challenges he could in the 80s, modern defenders have to be more precise and have less room for error. Similarly the change in the pass-back rule now means you don't have the release valve of just giving the ball to your keeper, so the pressure in possession has more consequences, mental lapses are more costly. Tempo seems to be consistently faster, so potentially more offensive plays that backlines have to deal with per game.
Captain Ramos is considered top defender by mass media due to his titles, don't you see Fixer ranting about Ramos on here for years? I think general consensus on PSD is that he is incorrectly labelled as the best defender in the world. Currently it seems Virgil van Dijk at Liverpool is playing really well, many users are raving about his qualities and vinnie consider's him maybe the best defender to ever play in the EPL.
You have to narrow the range you deem that there were apparently such a plethora of bad ass defenders in this romantic past, as you list Nasazzi (1920s-30s) and Moore (1960s-70s), that's a 30 to 50 year range, so does that mean modern defenders includes Scirea, Baresi and Maldini? Or are you talking about 2008-2018 compared to 1928-1938 and comparing that pool of defenders? Will we find better players in the older era, in a time when the sport was less professional? Did not some Manchester United players from the 50-60s have to work as coal miners to supplement income? Maybe that is why passing/scoring as you mentioned is a big part of modern defenders, since in the past some guys were too busy getting black lung instead of at practice
For the players from eras like pre 1950s, how many of the leagues were populated by a large pool of skilled players, since the money was lacking in the game? The system not yet in place to funnel youth talent and buy and bring together the best talent from all over the world. In my mind the legends of those eras made their names against a lower quality opposition, I just think like with any skills, practice increases competence, so aside from a few outliers, most were underpaid persons who needed to split time doing some other job just to make ends meet, hence less hours devoted to perfecting their skills, to me it seems reasonable that the general quality of all players was at a lower level compared to modern professionals. Hence I think players like Dixie Dean, Meazza, Nasazzi, Biscan may have been great players in their time, but who were their bread and butter opponents? Were the rank and file players they played against weekly in the 1930s equivalent to modern EPL quality or Championship level? All that stupid amounts of money in modern EPL serves to bring the top cream of the crop from every country across the globe, the concentration of skilled professionals at work I find hard to believe was present at the same level in 1930 even to 1980, I think it was around here you sometimes had a few (3?) foreign stars bolster a domestic team (or was that only Serie A with the 3 max rule?)...Really even in the Championship you have players who would be starters in Ligue 1, speaks to the quality present at the second tier of modern English football.
It's very difficult to compare the players since the environments are so different. I actually think if modern Sergio Ramos played in the 1930s he would be hailed as a wizard, how many midfielders passed like he could? Ocwirk was noted for it, would Ramos maybe too stand apart in that period? Surely his elegance on ball and ability to dominate aerially be a shock in the past, how many defenders were noteable to score as much as he does? He would blow peoples minds, his legend could grow to be immense when spoken in modern day, chumming up with Franco in pics lol, he would be the original Beckenbauer haha. Since red/yellow cards did not get introduced till 1960s(?) he would be king at duels on the field lol, the 20 reds he has in his career now would not be possible.