> Guaranteed income (GI) would at least buffer some of the anxiety. I could also see businesses knowing it existed would cut worker hours to part-time. But if part-time plus GI was enough then the worker has the power.

This is the biggest advantage I see, and shows why you wouldn't even need a living wage. You need a sufficient amount of money so that if a worker is being abused they can say "fuck it, I quit" and be able to live until they find another job. Being able to do that should prevent a fair amount of abuse in the first place.