the kind of shock that padding absorbs is not the kind of shock we're talking about here; we're talking about supersonically propagating pressure waves which create discontinuities in the pressure field, as well as the temperature field and the velocity field. to my surprise modern combat helmets are designed to protect against those to some extent, but padding is irrelevant to that; to shock waves, it's effectively a gap. the padding protects you from things that could displace the helmet until it hits your head, such as bullet impacts