I'm not advocating to use that formation as the regular nickel scheme but would like to see it once the offense lines up in a typical run formation.
I understand the argument, I'm just not sure I buy it.
It seems to be based on the idea the premise that a lineman is a better run defender than a linebacker, typically due to size reasons. IE, bigger = better. For interior defense, I tend to agree. For edge defenders (4-3 ends and 3-4 olbs) I typically don't. Especially with our glut of over-sized outside players.
Peppers is big for a 4-3 end, huge for a 3-4 OLB. Perry and Neal are typically sized 4-3 ends at 265-ish. All three set a perfectly fine edge in the run game, which is the primary run-defending job of an edge defender. Neal and Peppers offer enough as run defenders that both take some snaps as 3-technique tackles in dime and nickel defenses.
Consider: If there was a metaphorical gun to our heads and we were told to run a 4-3 defense with a front 4 of Peppers, Daniels, Raji, and Neal/Perry, how would you feel? Honestly, I'd feel pretty good. Why should we worry about that would be a fine
base defensive front as a
nickel defensive front?
I think too much is made about a supposed "soft" defense because play a lot of "linebackers." They're big dudes!
My primary concern with a 3-3 front is what I perceive as weakness in the middle. Obviously, it would depend on where the 4-3 ends lineup, but it strikes me as too easy for a Center-Guard combo block to move the nose tackle enough to create a clean enough gap for the fullback to cleanly handle the lone middle linebacker. Now the tailback is off to the races against a safety. Or cut the nose and have the Guard-Tackle combo block move the end, with the TE/FB doubling the outside linebacker. Have 1/2 of the combo leak off a clean up that MLB and again, ballcarrier is 1 on 1 vs. a safety.
The 3-3 looks to my eye, a better blitz centric pass-defense. The Bear/46 defense. 5 rushers (NT, E, E, OLB, OLB) against 5 offensive linemen.
I much, much prefer one linebacker-type per running back: The 2 ILBs in a 3-4, 4-2 nickel, 2-4 nickel, and the weak outside and middle backers in a 4-3. This lets the SILB/MLB blow up the fullback and the Weak outside/inside backer to clean up the ball carrier. There's a reason why that player is typically the smallest and fastest linebacker..