The o-line doesn't run block well enough to lean on the run game, no matter who's at RB
And the OC (McCarthy) is not good at Big Game game plans. The playcalling is conservative and suspect early in Big Games.
So Dak has to overcome a lack of a consistent running game and bad play calls or play designs.
Plus penalties.
Is Dak the answer? Maybe not. But I think Burrow and Mahomes would struggle with this roster and OC as well, let alone any other supposedly top-tier QBs (Josh Allen, Lamar, Purdy, Herbert, Stroud, Lawrence, etc.)
Throughout the playoffs, you see a lot of defensive and offensive plays that are a huge success simply based on the scheme. People are wide open, or it's the perfect call against the opponent's offense or defense, so then the play is a huge success (unblocked rushers, or a well-timed screen against a blitz). These RARELY happen for the Cowboys, especially in a Big Game. We don't have those kinds of OCs, they don't win the chess match, not great at the Xs and Os. Hard to win when you can't find simple ways to gain yards, and when the defense can't confuse the QB and the offense.