The 3-4 defense is built around linebackers. The Steelers of the last 20 years prove this better than anyone. They have run basically the same scheme since 1992, but the defense has flourished with stud linebackers like Greg Lloyd, Kevin Greene, Chad Brown, Levon Kirkland, Jason Gildon, Earl Holmes, Joey Porter, James Farrior, Kendrell Bell, Larry Foote, Clark Haggans, James Harrison, LaMarr Woodley and Lawrence Timmons. That really is an incredible list and it is even more impressive when you think that guys like Mike Vrabel and Carlos Emmons failed to become long term starters and left in free agency.
The 2013 Eagles had solid linebacker play. Maybe even good. But the group needs to get better if the 3-4 is to function at a high level. The biggest need is for depth as much as anything. Trent Cole, Connor Barwin and DeMeco Ryans all started 16 games last year. Mychal Kendricks was the slouch, missing 1.5 games. That durability is highly impressive, but it was also critical since the backup linebackers were so questionable.
No team is going to have stud starters and great backups, but you must have depth at certain key positions (dictated by what schemes a team runs). The Niners had outside linebackers Aldon Smith and Ahmad Brooks set as starters last April, but still wanted better depth. They signed free agent Dan Skuta and spent a third round pick on Corey Lemonier. That's a good set of outside linebackers.
The Eagles spent 2013 trying to see what they had. Barwin turned out to be a terrific free agent signing. He isn't a great pass rusher, but is a talented all-around linebacker. Trent Cole adjusted well to the new defense, but age has caught up with him and he's no longer a top pass rusher. Brandon Graham failed to shine in his move to linebacker. He had some good moments, but never played well enough to make you think he is anything close to a long term answer at linebacker. Chris McCoy was a legend in August, but gone by September. Rookie Travis Long is still a mystery since he was coming off a torn ACL, but even when healthy he didn't have the athleticism to be a top flight NFL linebacker.
I think the Eagles need to add a couple of outside linebackers this offseason. They need one high quality talent, be it in free agency or the draft. Then they need another player with athletic ability and upside. They could go for a lesser known free agent for this or spend a mid-to-late round pick. The point is to build up a group of outside linebackers, not just find a pair of starters. You can't count on Cole and Barwin staying healthy for every snap of every game, not to mention Cole will turn 32 in October and Barwin will turn 28 a few weeks later. And Graham is a free agent at the end of the year.
The Eagles must begin develop depth for now and talent for the future. 3-4 teams that don't rush the passer well from outside linebacker are going to struggle.
As for inside linebacker, that is a more complicated subject with the Eagles. They have some young depth in place. The team has high hopes for Jake Knott. Emmanuel Acho played well last summer. Najee Goode took the field in place of Kendricks last year for 1.5 games and showed serious potential. There is also Jason Phillips, who tore his ACL last year and never got on the field during the season. The Eagles like Knott the most of this group, but he was an undrafted player for a reason. It would be great for him to pan out, but you can't count on it. The Eagles could use a talented/athletic backup on the inside.
When did Noah build the Ark? Before it rained. The great Steelers linebacking corps of the last 20 years were built on the move. When a player got hurt or left in free agency, his replacement was often already on the roster. The Steelers kept an eye on the future and made sure they had plenty of good linebackers.
I hope the Eagles steal that idea and add some talented linebackers this offseason. They could get away with having the same starters from 2013, but this is the time to build depth and prepare for the future. And I don't think anyone would complain if the team added a top flight pass rusher who could challenge Cole for playing time right away.