Again, a business does take into account if it has part time employees and full time employees as part of the equation when they build in their pricing. Just like they take into account part time cooks and full time cooks. Their managers. Their food costs. Your point made no sense about that. When you eat out at a place that provides healthcare to some staff, you are paying for their healthcare on your bill. Period.
I started bussing tables when I was like 14 in a diner, and after I was 18 I waited in about 9-10 restaurants, from diners to a chain (TGIF) to a couple nice ones in Manhattan. And talked to many waiters, especially in Manhattan, about everybody's different experiences with all their previous experience. I have never been in one or talked to anyone where the waitstaff did almost no work and made all the money.
Everything varies by type of restaurant, but in general nothing you say stands true. You gotta hustle to make money. If it's a cheap diner you are running all your food and the checks are low price points, so you gotta work your ass off to make money. Swing shifts are 10 hours long of which half is spent running around like a maniac juggling a million things. Also you have no food runner there, and often bus your own tables because busboys get swamped. In a chain you usually get a runner, but you need to also run food. You are expected to upsell. You are not making money if you don't do work. You only make money if it's busy, and when it's busy, you work. In a nicer restaurant in Manhattan, that place filled up every night at the 6pm seating and the 8pm seating, and on weekends the 10pm seating too. It was madness in those places. The nicer the place the more you have to know and also upsell and you can't make mistakes. It's a lot of mental acuity and being on your feet. In those places you usually have back waiters, but you can also bring food to tables.
And I have always said to people when I talk about my restaurant experience, is that cooks are underpaid. It's crazy in some of those kitchens what the cooks do every night. I was a back waiter in one place in the city, I always say those guys deserve a good paycheck and healthcare. But that's socialism to a lot of people, including the customer in the OP.