I've thought about this, and starting with Julius does lull the defense into thinking they their current dedication to stopping the run is adequate, they can sit back on their heels and defend the pass.
Barber steps in and throw them off balance, so they either overcompensate for the run, or are just completely off guard and give up some big rushing TD.
What's going on right now is working.
The other way may work too, but...
It's working right now.
Also, Julius did tear off that 77 yard run against the Saints. He was on that night Dallas should have stayed with the run longer. If Julius gets a little more reckless, he'll tear off a lot more long runs, like he did his rookie year against the Giants and Seahawks.