As a consumer, I think it makes more sense to have the percentage by volume. Firstly, it makes the general pattern of alcohol content much clearer so we get a better intuition of what we’re getting into. Beers generally hover around 5%, wines at 10-15%, and spirits at 20% and above.

Building on that, people don’t generally remember the volume of pure alcohol they can handle, but they do remember, for example, that three glasses of wine is the most that they should drink. If you’re presented beer, then along with your intuition of their relative alcohol content, you can easily approximate that you can handle about twice as much volume since it’s about half the alcohol by volume. And similar if you have spirits, then you can reduce that volume to half or less.

How would you estimate it given a volume of alcohol instead? I know I can handle three glasses of this one particular kind of wine. If I have another type of wine with a different alcohol content and different bottle size, I’ll have to math out how much alcohol will be in my glass: (Volume of glass)*(total alcohol context)/(Volume of wine bottle). Most people would give up before even trying to come up with this formula. Now how much alcohol did I have the last time when I had three glasses of wine? The bottle said something like 80ml of alcohol. But how big was it? That’s two large numbers that you need to remember, and since they’re so different from one bottle of wine to the next, you likely don’t remember any of it.

Secondly, it affected flavour. In general, you can taste how much alcohol is in a certain drink and that depends on the relative volume of alcohol, not the absolute amount.