There are two categories of quarterbacks in Cowboys history. There are those who could and those who couldn't. In both cases, the team was good enough to go all the way.
Don Meredith couldn't
Danny White couldn't
Roger Staubach could.
Tony Romo couldn't
Troy Aikman could.
Dak Prescott.....?
All of these quarterbacks had their opportunities with teams that were capable. The ones that could were the ones that made those handful of plays that were the difference.
Even Trent Dilfer made those few plays when the Ravens won the Super Bowl in the 2000 season. In the playoff game against the Titans, he only completed 5 passes but one of them was a 56 yarder to Shannon Sharp to set up their first score when they were down 0-7. The game was tied 10-10 in the 4th quarter until the defense/special teams had back to back scores
We know the opportunities that were there, Meredith against the Packers, White against the 49ers, Romo against the Giants and Dak against the Packers.
It is the ability to makes the plays that must be made that separates QB's. Dak will be considered a can't until he can. Allen is in the same boat.