I guess it depends on your definition of "dominant."
To me it's more than just scoring points. When everyone knows exactly what you're going to do and game in and out they still can't stop it, that's dominance. When you roll up over 400 yards on the best defense in football, drop 27 points on their heads and do stuff like march 90 yards for six, multiple times, that's dominance. People keep saying the Cowboys play close games, but the team has the highest point differential in the league. Is that a trait of a dominant offense? Hobbout 9-1?
I think the fact that Dallas runs the ball, racks up 400 yards and wins by 10 points every week instead of throwing for 450 yards and putting up 50 points once in a while mutes peoples' impression of the team's offense. If Tom Brady and and the Pats were 9-1 and going for 400 every time they step on the field, we'd all be slobbering over how dominant they are.
The Cowboys are playing old-school power football, running over teams and imposing their will, beating their opponents into submission. To me, that's beautiful football. And that's dominance.
