Baseball’s modern era began with Babe Ruth. Pro football’s modern era began with the Super Bowl at the end of the 1966 season when the champions of the two professional leagues played each other. You can compare, but not equate, football teams from the pre-Super Bowl era.
The 1940 Chicago Bears "Monsters of the Midway" were the best team of their time, but they would stand no chance against even a mediocre college team of the 21st century. Changes in rules over the decades changed game plans and the size and skills of players. For example, those Bears of the 1940s and even Paul Brown’s great Cleveland Browns teams of the 1950s with Otto Graham at quarterback wouldn’t be big enough or fast enough in the game that has taken shape in the past few decades.
Expanding rosters made the strategy more sophisticated: a second tight end near the goal line, a third and even fourth wide receiver on third-and-long, or a fifth or maybe sixth defensive back in the same situations.
The day where a single player, say Paul Hornung, was called on to run, block, pass, catch and place kick is long past. A player such as Chuck Bednarik, star of the 1960 Philadelphia Eagles championship team, who could play well at center on offense and middle linebacker on defense, became a relic. Pro football turned into a game of passing and pass defense, a game of specialists.
That’s why the modern era of pro football featured the best NFL teams ever.