They would have the same coefficient of drag, correct, but the air resistance would end up having more effect on the lighter mass of the hollow sphere, so it would be slightly slower to fall.
Archimedes principle here is accounted for in the different weights. Everything that you can put on a scale is already being acted on by Archimedes principle in air.
Did you really just tell this person dedicated to CS and looking for advice that there's no hope and they'll probably kill themselves? Wtf