Anecdata, but every alcoholic I knew was self-medicating, so I suspect that the money itself from BI won't have much direct impact on alcohol consumption. OTOH, unemployment is a huge trigger for depression, so BI could go either way depending on how it's accepted socially.

OTOH, I do expect a good majority of basic income recipients to waste their time on stuff that tickles the meaningfulness receptors in the brain: video games, social media, and other easy tribe forming activities such as sports fandom.

But I agree with your basic point: you don't need very many geniuses and artists supported by BI to justify a large number of freeloaders IMO.