Avi8tor, sticking with steady winds and ignoring the added complication of gusts or windshear for the moment:
If inertia were groundspeed related then my paper aeroplane flying round in circles in a railway carriage travelling at a constant speed, would be affected by it's groundspeed, but it isn't.
I'm no physicist, but I think momentum/inertia are relative to whatever you choose as a point of reference, and the appropriate point of reference for studying the behaviour of an aircraft flying in a parcel of air, is the parcel of air. The momentum of the aircraft relative to the ground may suddenly become of interest though, if the aircraft contacts the ground.
THAI TUN