I don't think there is much between Maradona and der Kaiser tbh. The thing is - both revolutionized the game and were absolute leaders on the pitch. Both you can build a team around and were extremely talented individuals - way ahead of their time - in the same sense Di Stefano, Pele and Cruyff were before(alongside) them. There isn't objective measurement you can use as one is defender/midfielder the other is playmaker/attacker and both have different responsibilities.
Beckenbauer would easily be worth as much as Messi/Ronaldo in todays football for one simple reason - there isn't a player like him(if ever was) and anyone remotely close to what he was doing on the pitch. In an era where players like Stones and Walker are worth north of 50m pounds and teams are starving for a world class defensive player you can argue that a player like Beckenbauer is even more rare commodity.
Xavi should be very close to that tier as well, along with other midfielders like Didi, but to me by no means Xavi is a lesser player than C.Ronaldo or less important to his team(s).
It's all subjective, depends on how do you rate them and usually attackers always take more credit, but Beckenbauer is a multiple Ballon D'or winner (the only defender to achieve that) in an era his competition was other all time greats like Cruyff and Muller, along with several others. That goes to show how high rated he was a the time.
