Before Galileo, and ever since Aristotle, many people believed that heavier objects fell faster than lighter objects. That might be true where air impedes light objects, such as feathers, but many people believed that even in the absence of air heavier objects always fell faster, and it was commonly assumed that, heavier cannonballs fall faster than light cannonballs, even in the absence of any scientific data. The beauty of the scientific method comes front and center in this simple experiment conducted on the surface of the moon by Apollo 15 astronaut Dave Scott.
Just to be clear, Air "impedes" all objects based on their relative profile and aerodynamics. Gravity pulls on all objects of equal mass the same. A feather falls more slowly because of two reasons:
1. it's wide flat profile relative to mass incurs more wind resistance compared to a round cannonball
2. it has less mass
Thanks for the clarification, Dave. I was sloppy.