IMO, there's simply fix vs zone blocking - quit stunting so much
No, they cut way back on stunting starting in the preseason.
Stunting is not the core problem; although it does make things worse.
The primary way the Rams and other teams have attacked the Cowboys with Zone Runs:
Start an outside zone run to the side where the 1tech is aligned.
RB keys on the 1tech and backside LB to see if they over-commit or under-commit to the outside.
If they over-commit outside then the RB cuts back inside and vice-versa.
The RB knows how the OLine will block those players. The defenders are moving laterally. Blockers just need to get between them and the inside or outside. As long as the RB and OL "read" it the same way, it is hard for those 2 defenders to ever make the correct decision on inside vs outside.
In 2018 the Pats were running a 4-3 base defense.
In the Super Bowl Belichick swapped the OLB and Nickel CB positions.
Example: Slot WR outside LT.
The LB normally on the opposite side moved outside the LT.
The Nickel CB moved to the opposite side (outside the RT).
With the LB outside the RDE, the RDE played the gap inside the LT instead of outside the LT. That gap was normally assigned to a LB. Against the run they are just flipping gap responsibility between the RDE and a LB (i.e. The LB outside the LT now has that gap).
Note: The 1tech is on the side with the RDE.
Now the outside LB's run responsibilities are always outside regardless of whether the RB goes outside or cuts back inside.
The MLB's run responsibilities are always inside.
The 1tech does not need to make a quick jump to the outside to play the outside run.
The obvious "catch" is coverage. The LB plays a short zone and can block the inside path of the slot WR. A Safety has to pick up the slot WR behind the OLB's short zone.
On the other side the Nickel CB will match-up with the TE.
That simple change completely turned the Rams precision blocking scheme upside down. Without success running on 1st/2nd downs, the Rams QB became a sitting duck against the Pats 3rd down defense.
The Pats often use 6 big LBs and 1 DT on 3rd downs. They move around making it difficult for OLinemen to know who to block.
This season the Pats are playing more 3-4 on 1st downs which makes it easier to play run defense and keep the Nickel CB on the slot WR.
The other thing the Pats do is to vary the exact positioning of DLinemen based on specific down/distance and offensive alignment.
They are very focused on whether they are head-up or shaded in or out relative to the OL they're facing. They often adjust by half a gap just before the snap.
If you watch the Cowboys offense on zone runs, just having a DT aligned a half gap over can make a huge difference on many plays. It determines if the OLineman or the DLineman has better leverage on that snap.