When accounting for air resistance, heavy objects do fall faster than light ones. They couldn't test in a vacuum back then, they only knew how things work here in Earth's atmosphere.

A similar size chunk of iron and coal would have done the experiment just fine. Any two objects of the same shape and size but significantly different densities.

If two objects have the same size and shape, the force applied by air resistance will be the same. However, if two objects have different mass, that same force will result in different acceleration.

The acceleration will be 1G minus drag. The Earth is sufficiently larger than anything one would drop off a tower so the weight of the dropped thing doesn’t matter at all

How does your model of the universe explain the hammer and feather dropped on the moon by Apollo 15’s David Scott landed at the same time?

Ed. There is an effect of buoyancy that will make denser things fall faster. It becomes noticeable in distances where the dropped items reach terminal velocity or on more dense media where buoyancy is more significant.

In air over short distances buoyancy is negligible, in vacuum there is none

minus drag

On Earth, this is the part that makes it so that objects do not fall at the same speed.

on the moon

This is the type of experiment they could not do 2000 years ago.

minus drag

On Earth, this is the part that makes it so that objects do not fall at the same speed.

That is incorrect. Drag affects both equally. The difference is caused by buoyancy, less dense objects feel more buoyancy