The biggest obstacle to comparison in sports is time. Measuring one player against another is nearly impossible if the two competed in entirely different eras. Try comparing Doak Walker and Reggie Bush, two of the best running backs in college football history, and you wouldn’t know where to start—though it’s hard to believe Bush wouldn’t have the edge in the open field.
The same is true of teams. There’s little common ground to anchor a comparison of today’s teams with ones from the 1950s or ’60s, when pass plays were scarce and some teams still hadn’t integrated their rosters.