>So the main/hidden volumes really works like a duress: you might destroy your hidden volume while using the main one under duress, but that does not apply when using the main volume while able to additionally unlock the hidden volume.

The problem is that if the main volume doesn't have any signs of activity, then that's highly suspicious. Why are you carrying around a laptop that's mostly empty and hasn't been used in months? Why is it that despite seemingly not being used in months, there's physical signs of wear, like scratches or dust accumulation? If you do try to make the main volume seem "used", you run the risk of accidentally overwriting your hidden volume.