I guess Baresi, Maldini and later Nesta and co. weren't all that great. The team tactics made them play that well and function as a competent defensive unit.
The first part isnt correct they were fantastic defenders, the 2nd part is. I'm sure that you also notice the resemblance in the names. Italian defenders that played for a Sacchi influenced Milan in a country that stood as a literal fortress for defensive tactics for decades. Would Nesta, Maldini etc have had a similar success, had they played elsewhere? Take both of them, take a defensive line of Maldini, Nesta and even add 2 legendary fullbacks of your favourite choice to that and put this defensive line into Pellegrini's City. Would City have an unbeatable defence now, because they have the most illustrious backline in the history of mankind?
Maybe, or maybe not. Because even though Maldini used to be an exceptional tackler who would probably come out with a victory in 2 of 3 direct 1on1s with a striker, he would still eventually loose the 3rd. And then so-called pundits and fairweather fans will give their superficial views on the situation and blame him for the lsot tackle. And when he gets blamed to often for loosing out tackles, then people would question his ability and talk about replacements instead of figuring "Why the fuck is Maldini facing so many 1on1s in the first place?" The reason is because not only defenders are supposed to "defend", but everyone is, defending is a collective effort. Defensive problems do already start with strikers or midfielders and most importantly the tactics that the coach applied to the team, and those faults of others will eventually lead to defenders finding themselves in unpleasant situations and getting scapegoated.
Of course defenders have their individual differences, but there is a limit to how much this should cost and there is a cost-benefit factor.
If you're some fucking sheikh in Abu Dhabi, you own multiple football clubs, planes and spend your day throwing sales representatives into a pool of imported alligators by pushing some botton that is attached to the ancient saracen-throne you are sitting on, then you can of course go all out and spend 100m on John fucking Stones and pair him up with Godin and Boateng, because you dont give a fuck about costs or benefits, but the impact might still not be the one you expected. Surely Boateng and Godin would probably do slightly better in a chaos-defence than a pairing of Demichelis and Djourou would do, but I wouldnt go up and pay 130m for those minor differences. I'd rather question the coach or the midfielders and even those who score or assist a lot of goals.
If the defence-mechanics of your team look right, then you could even win a CL or a domestic title with 2 Umititi's or some other 20m defender.
Then most probably someone will want to buy your Umtiti for 80m next season, thinking he's the new god of defending.
