I'm not making a "trendy" argument, I'm advocating an alternative perspective based upon empirical studies conducted by a world leading professor in the arena of drug harm. The index is based on criterion in a number of areas that are considered harm, either to the user or wider society. I assume some of those criterion - particularly in the categories pertaining to harm to others - are indirectly affected by prevalence but in the absence of clearly defined methods, it's impossible to say with any certainty. However, other criterion - particularly those relating to harm to the user - most likely relate to the level of the individual rather than the population.
It is important to compare, for example, the pharmacological profile of each substance. Alcohol has an incredibly complex pharmacological profile, displaying potent affinities for the GABA, glutamate (AMPA, kainate, NMDA), acetylcholine, adenosine and serotonin systems, as well as a capacity to influence transmembrane proteins such as calcium channels, which modulate the exchange of ions across the neuronal membrane. Cocaine, in comparison, is a relatively clean drug, in that it is a high-affinity inhibitor of the dopamine transporter (DAT), which leads to an accumulation of dopamine in the synaptic cleft, though it is also a relatively decent inhibitor of serotonin and noradrenaline reuptake. In considering such differences, one can begin to understand why alcohol has a much greater dependence liability than cocaine. That is, continued alcohol abuse invariably leads to the development of physical dependence, whereas cocaine does not - it tends to produce a psychological dependence. Sustained alcohol abuse can also produce a psychological dependence. Anyway, the point of this is that alcohol abuse produces a physical dependence syndrome by virtue of its pharmacology that, in certain instances, can be fatal whereas cocaine does not.
Consequently, discussions around drug harm are, by their very nature, incredibly complex and don't tend to lend themselves to soundbites.