Crystalline Carbon Allotropes are, like all crystals, laden with shear points. Generally substances that aren't crystalline are vastly superior in protection than crystals. Simply because they don't just shatter once you get to a certain point.

Likely, but that delves into theoretical situations, so suspension of disbelief.

No, it's the same kind of force distribution when you stab something and shoot something. That is sharp force trauma in both cases. (Depending on the kind of bullet, of course.)