I used the "grade" term to compare it to a regular steel bolt. Most people are not aware of material properties like you and I, so we need to use terms most people understand.
I've snapped off many 5/16 stainless bolts with a 3/8drive ratchet. And others I've impacted tight, or had to use a long breakerbar to remove.
You are correct in saying the exact material dictates its strength. (But your stainless example said exactly what I did as far as grade goes)