Looking past Jerry Jones' overbearing atmosphere that handicaps every coach in Big D, the quickest way to improve the Cowboys is to build a strong running game!
The Cowboys do not have a commitment to run. They keep checking out of it on the whim of the QB. Dallas has to be able to set a slow paced game that eats the clock, whenever they want. Playing against a high powered offense like the Broncos or Saints, you have to have it! There's a much better chance that the slow methodical pounding offense wins out against the quick strike offense.
Why? The DEFENSE is more rested with a run-centered offense. Strength and conditioning coach is not entirely to blame, each incomplete pass or clock stopping play means more time on the field for your defense.
It's not a good formula to keep gunslinging the ball around, but Dallas keeps going to that, even when their backup QB has not had extensive reps with receivers for more than one week.
Sometimes, I think it would be great to just go goaline with a NT-sized fullback and pound the opposing defense into submission. I doubt Romo would check out of that just to pass it to Tyron Smith.
They must add talent and find ways to minimize the injuries. This is more important than the coaching staff.
One way to lower the probability of injuries is to eliminate older players and replace them with younger players. Ware, Austin, Hatcher, and Spencer should be allowed to move on. Ratliff is already gone.
By cutting Ware and Austin and not re-signing Hatcher and Spencer, they can afford to sign YOUNG free agents. They can get 2 top free agents for 3 to 4 mid-tier free agents if they cut Ware and Austin.
It does not really matter how long the offense holds the ball if the defense allows the other team to score on every possession. You can have one 58 minute drive to score a TD and the other team can have one 2 minute drive to score a TD. The result is a 7-7 tie. If you ever get behind when playing an offense like the Broncos, you'll never be able to catch up with a slow methodical offense.
The offense that gives you the highest probability of scoring at TD on each possession is the best way to win. That is usually an offense that can pass or run effectively.