This is completely false. The standard measurement bars use is called the "pour cost" which is inventory usage(in cost) divided by sales. The pour cost average for a bar is between 18-20%. That's a gross margin of 80 to 82 cents on each dollar a customer spends on drinks. That's a pretty spectacular margin. A well-run bar on a busy night is practically printing cash.

A bud light at a bar is like $12 now at most bars. The case at the gas station across the street is $18. The splash of coke in the $10 well drink that begins with a cup scooped full of nearly free ice must have been about five cents of syrup and one cent of CO2, the pour probably came out of a bottle that costs like $15. Maybe that maxim was true back in the day when people could actually afford to get drunk at bars, but not anymore.

I run a restaurant. A regular domestics (bud, miller, coors) run about $1.10 per can/bottle if you get a single case. Busy bars ordering 10 cases at a time will be getting discounts. Unless you're going to the shittiest dive bar in town, a $3 domestic bottle is nearly 200% markup.

This is the opposite of true. Not even factoring in the cost of labor and everything else related to having a kitchen.

As someone who spent a LOT of time working in/running professional kitchens in the US (NJ specifically) I would just like to say:

CITATION NEEDED