I just gave you the data
But having been around at the time, the game did not change that quickly from 1972-73 when the Dolphins ruled until 1977-78 - we are not talking about the 1962 Packers playing the 2007 Patriots
And to the extent the game did change during that time, the Cowboys did not take advantage of the rules changes as much as the 1978 Steelers did when the new rules were implemented. So it is not as if the Dolphins' 53 defense, which relied on scheme as well as talent, would have been outmoded against the 1977-78 Cowboys offense (as opposed to Landry's Flex defense, which was designed to stop the Lombardi sweep, that Bradshaw shredded by throwing against in SB XIII since the pass rush out of the flex by the defensive end was nil).
Bottom line is Dallas had the good fortune to play in the NFC in the 1970s when the AFC was clearly the superior conference and its record was inflated accordingly.
1977 Cowboys were defeated convincingly by a Steelers team that was the worst of the 1974-1979 teams and had the good fortune to play Denver rather than the Raiders or Steelers in the Super Bowl that year. Then they did not even get home field advantage through the 1978 playoffs - we are not talking about the 1984 or 1989 49ers here.
And with regard to how could they possibly handle Tony Dorsett, when OJ Simpson (who had some speed of his own) rushed for 2000 yards in 1973 he rushed for only 175 in his 2 games against Miami
https://www.pro-football-reference.c...7310210mia.htm
https://www.pro-football-reference.c...7311180buf.htm