They do not make less than minimum wage on paper, by law they need to earn at least “regular” minimum wage when tips are combined with their hourly pay.
I think the career is physically tough, and gets harder as you get older like most physical jobs. Most restaurant hours are long, can be very late, can be during the holidays when the rest of the family and friends are off, and working with the public like that can be stressful and some customers are downright awful. However, I know plenty of people who make a good living waiting tables. Working in high end restaurants can be great money and the atmosphere at work is very nice. The comradery in the restaurants can be very good, although it can be bad also of course. It can be exciting as the restaurant open for meal service, like lifting the curtain to a production. One big negative is it is not uncommon for people in the restaurant biz cheat on their spouse, do drugs, and drink. I am not saying it is the majority of people, I don’t know the stats, I am only saying it is not hugely uncommon. You see it more in some parts of the business than others.