I didn't see the Packers getting huge yards running up the middle. The one play where Jones started up the middle and bounced off the pack and ran around the left side for 25 yards was not the fault of the middle of the defense. They did their job. The pursuit did not cut off the cut back. This has been their problem with the run game. The pursuit is taking bad angles, over-pursuing, getting cut off and sticking to their blockers, and otherwise failing to guy a helmet on the ball carrier.
This defense is never going to be one that stuff the run for 1 or 2 yards every down. We will se some 4 and 5 yards carries up the middle because LVE plays deep and is slow to get up into the hole. All the LBs, including Parsons, get caught up in traffic too much. Now one is slashing through the blockers to get to the ball carrier.
Stopping the run is a team effort. Everyone has to do their jobs to prevent RBs from cutting back, jump cutting to a different gap, allowing the QB to escape the pocket and run for a 1st down, etc. To me this is why the Cowboys are not stopping the run. Against Green Bay, they were less aggressive and it hurt the pass rush.