Tomlin and Butler generally employ 2 down linemen. They leave the other 5 of the front seven to mask what their doing in terms of their rush or coverage responsibilities. Unfortunately, this means only 2 guys get a straight on, immediate power rush at the defense. The Offensive line has time to react to the other fellows on the defensive line that are going to engage them. With only 2 clear defensive linemen, it is painfully easy to identify, isolate and neutralize them.
This defensive formation by its nature allows the offensive line to dictate engagement. If it's a run play, the offensive linemen have time to blast off the ball and engage a defender before that defender can get into a low, blocking/shedding stance. If it's a pass play, the offensive lineman has time to identify who's blitzing and who's dropping into coverage, allowing them to slide and cover as necessary.
The one strength of Tomtler's scheme is that the QB has a harder time with pre-snap reads, assuming the defense doesn't give too much away, or they don't get tricked into giving their responsibilities away with a hard count.
Ultimately, the 2 down lineman thing is failing in the current pass-happy NFL because it doesn't force the offensive line to adapt to the defender, rather it does the opposite.