Dominos is arguably quite a bit larger than the mom & pop restaurant I did delivery for, but... for us it was break-even or a very tiny loss. I don't remember exactly the number, but delivery was $5; $5 charged to the customer, $5 paid to the driver. I think it was waived for large orders (>$100?), but those were pretty rare. Tips were all for the driver as well. On a good night, you could make $20-30/hr; on a holiday night (New Year's Eve was my favourite), it'd be more like $40-$50 once you factor in the tips.

Was it overall a living wage as a sole source of income? No, not at all. There was usually only a small window every day when people actually wanted delivery. Was it good money for the number of hours worked? Sixteen year-old me sure thought so!

Delivery is profitable for dominos. But the real money, well that is in garlic bread.

all restaurant business is just a ploy to get people to buy soda

No, it's not. The most you can charge for a soda is $3 around here. Even if you make 95% profit ($2.85), pretty much every single food item will make far more profit. A $12 salad will net you $9, a $15 dollar pasta will probably net you $12, a $40 steak will net you $20, and so on.

Gross profit matters far more than profit margin. Also the best way to be profitable is to increase sales relative to fixed costs, rather than trying to squeeze every dime out of limited sales.

Alcohol and coffee are also helpful.