You said,
"Take a quarter, hold it in your hand in front of you. Let go. It falls at 9.8 m/s because of gravity."

And I am saying that that's an assumption.
The reason the quarter will fall is because it is more dense than the air that surrounds it. Gravity is irrelevant. What you have just described is buoyancy and density.

Dropping a coin does not prove that gravity exists. It only proves that the coin is heavier than the air around it.

Watch the video from 13.31 to 20.24.