At 80 drives in 4U, removing the drives from racks is only going to improve density by a small percentage. Perhaps by removing any walking space between the racks you could bring it down to 180 square miles from 360. HDD are more volumetrically dense than tape.
Any way you look at it, a yottabyte is going to occupy an enormous amount of physical space.
Any way you look at it, a yottabyte is going to occupy an enormous amount of physical space.