I liked Broaddus' reasoning: You don't wait until there's reason to take Dak out, and in so doing, inherently plant the seed of doubt in his head for when he comes back after Romo's finished his Dallas run. For Dak's own sake, you put him in a position to be the hero, either coming back in this season after Romo falters, or, better, coming back in next season after Romo exits the roster.
All of this momentum stuff is bunk. Like I think Jimmy Johnson (?) is noted for saying, momentum is a matter of what you do on the next play. Dak is clearly capable of playing at a high level... maybe/hopefully over time, we'll find he's capable of playing at the highest level.
But Romo is clearly capable of playing... now... at the highest level.
And so I like my reason better than Broaddus, though admittedly it is more short-sighted, but hey, you gotta strike while the iron is hot... these opportunities don't arise every season...
Who do I feel more confident about starting a playoff game? Who do I feel more confident about leading us into a Super Bowl?
It's the guy with the history of playing at the highest level... the guy who stands with the best QBs in NFL history in his high pressure 4th quarter body of work.