I haven’t watched the video yet, but will do so soon.
My thoughts on particle shape for coffee being important is based on readings of grain shape for gunpowder. Just replace burned with extracted and the parallels will be more clear.
For ball shaped gunpowder, the exposed surface area decreases as the propellant is burned. These are called regressive grains.
For tube shaped gunpowder, the exposed surface area stays relatively constant as it is burned. These are called neutral grains. (Note: interestingly blood cells also have a relatively neutral shape).
There can also be progressive shapes, but I don’t see how they can be created in coffee.
Flat disks would also be regressive, but not as much as balls.
Ideally, I think we would want a more neutral grain shape for coffee. Failing that, I think we would want to adjust flow in relation to how much extraction is taking place (hence the popularity of decreasing pressure profiles).