I agree to an extent. The DL is valuable, but as the league becomes more and more a passing league, its that pass rush that is most important.
With the rule changes, and emphasis on turning secondary play into asking permission before hitting, there is almost no defense that can stop a 2 minute offense by covering. 4 passes to get 10 yards is almost unstoppable unless you pressure the QB.
A relentless pass rush that not only gets pressure but influences the play calling of the offense (ie get it out quick to beat the rush) is the only way to be a really excellent defense in the NFL under the current rules and emphasis.
The other problem is that offensive holding becomes more and more legal. Scheming a pass rush doesn't work consistently either. You need skilled pass rushers who can win one on one battles, and deal with legal holding.