Honestly, it IS both. If you are working at a high end, popular restaurant, on good shifts, you can make a decent income waiting tables. There are some Disney World servers who - pre-Covid - were rumored to make around $100,000. Those people would be really screwed by a “must pay minimum wage” and get rid of tipping culture.
On the other end, you have someone who gets weeknight bar close shifts at a 24 hour Denny’s. Half the tables don’t tip at all, and there are nights where its you and the cook there all night. By federal law, the restaurant is required to make up wages to the minimum wage - not per shift, but per pay period. But its one of those laws that is seldom followed.
We’ve always tipped very well. We are now tipping well for DoorDash and when we do curbside. We have done restaurant meals during Covid - outside - and tipped extra then as well. Heck, I tipped at a restaurant that was hosting a Toys for Tots drop off and I didn’t even order food, just dropped off toys. I don’t tip at the Starbucks counter.
Pre-Covid (and hopefully post Covid) one of our favorite restaurants had a note on the menu. All servers were paid a living wage (Knowing someone who worked there, $15 an hour, and a small staff of servers so you got your hours - the other problem with that sort of job is that three four hour shifts a week isn’t going to pay your bills). Tipping was appreciated, but at your discretion. We always had excellent service, we always felt we were getting good value (it was an expensive fancy place, but wonderful food), so we always tipped on top of that. I REALLY hope they make it through. (They aren’t a Door Dash type of place).