In 17 regular season wins, Chip Kelly opponents are 87-152-2 (36 percent). In 9 losses, opponents are 79-46-1 (63 percent).
Checkmate.
Jason Garrett's first 26 games:
In 14 wins, his opponents were 99-125 (44 percent).
In 12 losses, his opponents were 110-82 (57 percent)
And these numbers are hugely skewed because of the 2010 season finale, a 14-13 win over an Eagles team that finished 10-6 and had already clinched the division and didn't play any starters (Vick-McCoy-Maclin-Jackson, etc.). So that's a cheap 10 wins that go into Garrett's tally.
If we take that out, we're looking at nearly identical numbers, and there's no real discernible difference even with it factored in.
Here's another statistical comparison:
Chip Kelly in 26 games: one division title, one playoff appearance, one winning season.
Jason Garrett in 66 games: none of the above.
Checkmate?