I'm kinda mixed on this one. Although I can see your point about Josh not playing as well in inclement weather it's the D that concerns me.
They've proven all season stopping the run is problematic. In bad weather it only gets worse as it favors the more proficient running team (Indy,NE). Is it a coincidence Devon and Josh ran all over Atl yesterday in the snow?
So to me weather is a factor, but not because of Josh's play. It's our D's inability to consistently stop the run which puts more emphasis on Josh to perform.