YPG is horrible. YPC is far from perfect but it's a much better indication of a decent defense.
I think it was last year the top 10 tens in allowing YPC were almost all in the playoffs.
This year seems to be pretty split with some of the stronger "contenders" allowing over 4.5 YPC. Surprising.
The Bills and Jags currently stand at 4.3, that about sums it up. Far from impossible even with Mount Dareus, much easier to climb than Mount Washington!