Best NFL defenses of all time?

[Bored5000]

I am shocked that people on here don't consider the 1991 Eagles defense among the best of all-time. I am not saying they were better than the 1985 Bears or the Steel Curtain, but the 1991 Eagles almost always comes up in discussions of all-time great defenses. Sometimes it is listed at number one. The '91 Eagles defense is at least in the discussion with any all-time great defense.

As mentioned, the 1991 Eagles led the league in fewest yards allowed against the rush, the pass, and overall. The squad led the league in sacks, forced fumbles, and takeaways. What exactly constitutes an all-time great defense if that's not it?

It was the defense's fault the team did not make the playoffs? James Joseph led the team in rushing that year with just 440 yards and four different players took turns at quarterback after Randall Cunningham was lost in the first quarter of the first game. At one point, the team went 11 straight quarters without scoring a touchdown. Reggie White should have been playing quarterback? Jerome Brown at running back? Andre Waters at flanker?