Gone are the days when offensives lined up predominately in the I formation, and defenses played the majority of the game in their base defense. I always find it comical that the NFL still votes for an all-pro fullback when so many teams do not even have a true fullback on their roster.
Does it really matter then? It does when it comes to personnel. The Steelers have drafted and brought guys in to play a 3-4. There are basically three defenses that the NFL employs. The over (what we think of as a 4-3), the under, and the 3-4. The under defense employs the same basic personnel as the over front, so what really separates these defenses are the players that make up the front 7.
The Steelers could, theoretically, line up in a base 4-3. The two inside defensive tackles would be Steve McLendon and Cameron Heyward. The best defensive linemen is your 3 technique, and that would be Heyward. Defensive ends could be our normal outside linebackers and maybe Stephon Tuitt. You would probably take Jarvis Jones, make him a Sam linebacker, have Lawrence Timmons play the Mike linebacker, and either Ryan Shazier or Sean Spence play the will. You could then play the under front by taking your Sam linebacker and play him to the strength.
The Steelers could do this, but will they? Beyond being a different skill set, these are different reads and run fits. It would require guys to play positions they have not for some time. The Steelers do employ so over front principles when playing their nickel package. But, that is done from the base of a 3-4.
If anything, in my opinion, the Steelers are looking to simplify things on defense, not start over. Over the last five years, the Steelers have gotten huge contributions from players on the offensive side of the ball that have less than 3 years of experience. As we have heard time and time again, the Dick LeBeau defense takes most years to master. If the Steelers are looking to get more out of their younger players on defense, then changing the base defense makes no sense.
The reason that everyone in the NFL plays, basically, 3 fronts is because they have stood the test of time. If there was a perfect defense, everyone would be running it. What is more important than scheme, is getting players playing fast and confidently within the scheme. The Seattle Seahawks destroyed the Denver Broncos in the Super Bowl playing what they normally play. The players were emphatic after the game that they did nothing special; they did not trick Peyton Manning. Instead, they out-executed them. As was pointed out in Steelers Film Room, the Steelers had a mental mistake at the worst possible time. Moreover, after many losses, players have been quoted saying that big plays came as a result of people not being in the right place. As a result, the Steelers will have someone new in 2015 making sure that everyone is in the right place.