Chip Kelly's offense is a gambling offense. By that I mean it gambles that it can get first downs consistently and that if they can get a lead on a team, they can get more aggressive on defense.
For example, it's no different than if a team never punted and went for it on 4th down every time no matter the field position. If that team has a game where they convert 8 out of 10 4th down attempts, they come out looking like a dominating offense. If they convert 1 out of 10 4th down attempts, they get exposed and labeled a gimmick offense. It was the same with the old run-n-gun offense. It was high scoring as well long ago, except when it didn't work, and when that happened, it looked really bad.
The problem for Dallas is that it cannot consistently stop other teams on 3rd downs. That plays directly into the Eagles scheme. Dallas can beat the Eagles in Philly, but they can also lose just as easily. No matter the outcome, it's a gamble and whether the Cowboys win or lose next week, it won't make them a better or worse team than they are now. A win will help with their playoff chances of course, but beating the Eagles won't be any real gauge as to how the Cowboys would/will do against other playoff teams.
The bottom line though is the Eagles may beat Dallas and may get into the playoffs, but their gambling offense won't last against good teams over several games.