You're mistaken---it was Prohibition that boosted the poularity of hard liquor relative to beer and wine. And this is simple economics: criminalization boosts the relative value of highly-concentrated goods over less-concentrated goods.
Correct. During prohibition distilled spirits, brandy, and beer rose in price by 400, 450, and 700% respectively.
Although the effects of 1 shot of liquor is the same as 1 beer, the chance of getting arrested while supplying beer was higher --it makes beer more costly.