Every team with a winning record will have a lower SOS because they are giving their opponents losses, a 1-2 more wins for you opponents to match-up with the teams with teams that are 8-3 instead of 10-1. The Philly opponents so far this year have won 48 out of a possible 121 games, or .405, if we were to take out the "Well Philly beat them" argument then it's 47/110 games, taking out the win against Philly as well, which is still only a .427 SOS. Let's compare that to some other teams shall we?
(9-2) New England: 57/121 (.471) - 55/110 (.500)
(9-2) Minnesota: 59/121 (.487) - 57/110 (.518)
(8-3) New Orleans: 67/121 (.553) - 64/110 (.581)
(9-2) Pittsburgh: 56/121 (.462) - 54/110 (.491)
(8-3) L.A. Rams: 56/121 (.462) - 53/110 (.481)
(10-1) Philly: 48/121 (.405) - 47/110 (.427)