Defensive mid-field were always around. They use to get acknowledgement, but not as now. Victor Gamaldo, Bert Grell, RuggedTom Davis(Paragon), Leon Carpette,Brian Rigsby, Chinapoo and even Sedley Joseph(old half back/center) used to play that position. Sedley was a very good distributor of the ball, especially the counter-attack long ball.
I think this position got real important after the 74 WC. Holland caused everybody, especially Brazil to change the way they played. the socalled "jojo bonita" went out of the window for a while. They employed men like Toninho Cerezo, Junior, to name a few to counter Holland and the Euros physical attack brand of football.