It seems like you're only classifying the physical labor as "work", and ignoring the skill and effort it takes to do all the stuff a waiter/waitress does. There's a lot of memorization involved, being able to answer a lot of different questions, making sure the meal gets delivered as soon as possible, with the right stuff, and checking back at the correct times to see if anything else is needed, including drinks. It's a lot harder than it seems.

The bussing jobs are a lot more physical and there's less to think about.

Also, he gets 10% of the tip... But where does the rest go? You're assuming the other 90% goes to the waiter/waitress, but it's possible a large portion of it goes to the kitchen staff.