Hi:
I wonder if it is really an issue between the Welsh and the Cornish?
We use crushed granite here, the size of a watermelon seed, for our mixes and they have lots of sharp edges as you can imagine. For certain plants like Hyeronimiellas, Chilean Rhodophialas, desert Habranthi, Ferrarias, etc., we grow them in pure crushed granite and they thrive in it.
It is mentioned that the soil become compacted which points to the presence of dust as the cause of the bulb rotting rather than injury by the sharp sand