The Eagles are just built tough, and they rarely beat themselves, with penalties and such. Yes, the occasional turnover, but it's football, that's unavoidable.
I think they are helped immensely by having the Tush Push be an automatic 2 yards, as any team would be. It's a HUGE advantage, especially late in games. It changes the whole complexion of the game when a team only really has to get 8 yards in 3 downs. It forces the defense to call a different game and manage situations differently. Hec, on 3rd and 5, that's a running down for the Eagles...because if they can just get 3 yards, then they can line up and get 2 yards with the Tush Push. It transforms how the Eagles call their offense, and how a defense call plays to stop them.
Plus, it gives the Eagles more opportunities to score than other teams.
It's like a Madden glitch.
So, for Eagles opponents, they are going to really have to bury the Eagles by the 4th quarter, and outcoach them in the final quarter. The Bills had them on the ropes, but they got enamored with 1st-down running plays. In the 4th quarter, the Eagles were waiting for them, which set up too many 2nd and longs...and you can't live like that against the Eagles. The Bills should have used more 1st-down play action. In the end, the Bills simply expected Josh Allen to carry them to victory with his athleticism, instead of just calling a better game in the 4th quarter. The Eagles beat you with better playcalling, and the Tush Push.
I fear that the Cowboys aren't all that great at adjustments either, so in a close game against the Eagles, it's hard to see how the Cowboys would win...especially with the Tush Push as a 3rd and 4th down advantage. You need to get Philly into 2nd and 3rd and long to force the issue, which means you have to take chances on 1st down. The Cowboys won't be able to sit back and let the Eagles get 3 and 4 yards on the ground, else they will never be in position to get sacks and such. The Eagles present a real challenge for coaching staffs.