with the chemists selling useless cold medicine but the streets EVEN MORE full of meth-heads than before, obviously this particular "war on (some) drugs" measure is a pathetic failure.
That's also not how logic works, if you want to claim that this measure was successful you need to offer convincing evidence in favor of that. The benefit of the doubt doesn't go to failed war on drugs policies.
I'd imagine you'd still need a cost benefit analysis if this inquiry were done in good faith. Which in politics, especially when it comes to controlling drugs, it never is. The exception possibly being prohibition itself—but prohibition actually worked, in the sense that the rate of binge drinking dropped drastically. No such efficacy is obvious here and it seems like a really useful medicine.
The problem there is that alcohol is relatively high-volume, I mean a barrel of pure ethanol is still a barrel of pure ethanol. By contrast fentanyl for example can be effectively shipped, in commercial quantities, in the back of a sedan or human-portable luggage.
Stopping binge drinking meant reducing the amount of available alcohol, a substance requiring large scale shipping and production, storage and so on. Modern drugs really don't have that problem, and for the ones that do, synthetic alternatives would just take over.
Improving folks economic reality tends to lower drug use. We could try not further ruining lives by putting them into the "justice" system and instead close the gaps they fell through while helping them up.