And you ask a very good question regarding whether the libero plays with one stopper or two. I generalized there a bit admittedly and should have been more clear. You are absolutely correct that Germany employed Mathaus with Kohler and Buchwald - 2 stoppers..but there were other variations of it where you had one sweeper, one stopper and then still a more defensive #6 who would drop back and help when needed IF the team had more creative attacking tradional #8s and #10s. The Catenaccio style of the 60s and 70s had more of the latter. AC Milan did as well with Baresi the libero and Rijkaard the defensive midfielder (although he was about as attacking as a defensive midfielder got). Daniel Passarella was maybe the Godfather of this second type of system with Argentina.
So I guess teams did both, I should have said.
Your definitions of Libero and Sweeper are absolutely spot on. Augenthalar was more of a sweeper, Mathaus more of a Libero due to his earlier midfield background. The point I was trying to make earlier was that the reason I don't think the Libero would perform the requisite effect that WTM was suggesting in the OP is, the Libero still starts their job behind the CBs, not in front of them. So in essense, even if they are allowed to push up into space when possible, they are starting off the blocks further away from attack than a Mascherano or holding midfielder does. No matter how you slice it, the libero is the more cautious, defensive approach to having the more modern defensive midfielder sitting in front of the back four so it the libero would not make us more offensive than we are right now.
In fact my belief is the reason the holding midfielder and 2 CBs system evolved more in modern football is CBs have become better ball players and defensive midfielders are trusted with being more mobile, better at reading the game, and better at carrying the ball forward so they help a team become more "adventureous" than the opportunistic philosophy of the libero.
I too watched with great interest our 3 CB formation over the weekend and I couldn't agree with you more on how it looked on the pitch. It looked like Carra was sitting much deeper almost like a sweeper does in the middle, and Skrtel and Agger were very much spread on either side, much more than when we play with 2 CBs. Problem is, Carra is the most cautious defender we have, so he isn't going to push up too far or gamble too adventurously with ball at feet. His ball skills being what they are....he will sit back and spray passes around but he is not dashing down the middle like Agger likes to do...so we kind of lose the libero/sweeper effect offensively when Carra is playing down that middle of the 3 back formation. Yet, Agger is left footed and Skrtel is right footed so you have to say they were where they needed to be. I wonder if a Hyppia in the middle where Carra was playing would work out better because he is better on the ball and make those deep penetrating through passes like he served up for Torres against Everton. Interesting thought....
Your last point about AC Milan is another good one...and I agree. I think AC Milan adopted or tried to adopt what Holland was doing in the 1988 Euros with outstanding ball handlers in the flat back four...pressuring high up and condensing the pitch in defense...but spreading out wide and stretching the other team when they won the ball. It was sweet poetry watching that Rinus Michels team stroking the ball around the park slowly and casually, and then at the blink of an eye someone was cue rolling the ball to Ronaldo Koeman who could strike the ball like God!!
I believe that if you really wanted to define Rafa's philosophy...or the one he is trying to employ...its a marriage of the Sachi and Rinus Michels versions of "total football".