Inertia is a function of GS,
Whilst it doesn't alter the thrust of your post, that isn't strictly(or to be more precise,
necessarily) true.
Inertia, also known as momentum, is Mass * Velocity. Velocity, however, is relative to whatever frame of reference you choose. A body has a certain velocity reference the ground, therefore a certain momentum relative to the ground, but messuring it's velocity reference the air around it is just as correct.
Newtons (and Einsteins) laws are Universal. They don't somehow only apply to movement relative to out very small Earth.