Another way to ask this: how does hugelkultur logs/material compare with a similar volume/mass/cost of other material e.g. traditional soil.

My guess is it does pretty well: traditional soil struggles to retain water, which can be scarce and even when it's plentiful water is difficult to optimize for high density gardens, especially urban gardens.

If I understand the hugelkultur design, the sod/straw layer keeps the berm from eroding.