On the contrary: most tipped employees I know make substantially more than the untipped ones. The why is simple: price discrimination extracts excess value. If everyone's paying the same price, you lose some potential profit from people who would have been willing to pay more, and you lose some potential profit from people who aren't willing to pay the set price, but would have been willing to pay some still-profitable lesser price. By charging people based on their willingness to pay, you extract much closer to the maximum value.

Tipping is a price discrimination scheme that directly benefits the workers. That's a lot of value that can be captured, and any other system that a restaurant could use to extract that value would end up benefiting the owners far more.