OwenM :
It may be "the property that contributes most", but it is only one factor.
Which accounts for the type of blunting described in the above to such a degree that the rest of the factors are ignored. Hardness is also the critical factor in many durability issues. For example it directly controls the level of indendation through impaction, as this is exactly what it measures.
it's the steel that determines toughness, strength, and wear resistance.
Strength is very critical to RC they are highly linear correlated, small changes to RC can swamp out huge alloy changes. Impact toughness is also very sensitive to RC. A small change of 1-2 points of hardness can cause changes of 100% in toughness, larger changes can make an inherently tough steel very brittle, steel composition can however induce great impact toughness changes as well so it is also very critical in that regard. Ductility is also strongly correlated to RC but also dependent on steel composition in a similar manner to impact toughness.
Wear resistance and corrosion resistance are far more steel dependent, RC is only a small factor can can usually be ignored. Where it is a factor, it isn't the hardness directly that effects the properties but the underlying change in carbide content that the particular heat treating scheme induced. In particular for wear resistance, where Vanadium is a carbide former, wear resistance can be simplified to a direct proportion to the percentage of vanadium carbide as it is so much harder than the other carbides it swamps them all out.
In short, in many aspects of knife performance hardness is the dominant factor (edge denting / rolling) and small differences can induce large changes in the performance of the steel. In other areas of performance it is still critical and the right hardness is necessary to optomize a steels performance (impact toughness, ductility). Some performance aspects are also nearly independent of hardness (wear resistance, corrosion resistance and heat resistance).
The entire spectrum of performance becomes optimal when the steel is chosen which has the best combination of properties (which means the tasks for the knife have to be well defined and understood), the steel is treated to maximize these abilities, the blade ground so as to maximize cutting ability with the necessary functional level of durability and minimize sharpening time, and the handle crafted so as to be comfortable with the necessary level of security.
In any of these factors are significantly off, the performance of the knife can be gutted regardless of the rest of the aspects.
-Cliff