DoorDash et al. aren't innovators in anything other than creative contracting and marketing. There's no magic practical efficiency that makes their business work.
Source? At least according to this study[1] 92% of uber/lyft drivers in seattle made above minimum wage. True, this isn't exactly the same as for delivery workers, but given how fungible the two jobs are I think it's fair to treat them as approximately the same. Much more interesting is how much your earnings vary depending on your assumptions. The study calculated $17.40/hr by using pessimistic assumptions, and $23.25/hr using optimistic assumptions.
[1] https://ecommons.cornell.edu/items/161915a8-b0b8-4dc4-b5ff-d...
Where this falls down is trying to scale the business to less affluent people without some serious limitations. Pizza delivery places for example generally have a small delivery radius which makes a huge difference.
It's illogical to say a business is not sustainable because it dies after its been kneecapped by regulation.
It's illogical to ignore the size of the market and think that there should somehow be a need for just any number of drivers instead of the required number of drivers.
It's illogical to ignore that when prices to customers are artificially low, customers will consume more than when they actually have to pay for what they consume.
Since the driver pool has been paid for by vc funding rather than consumers, there are more drivers than needed. A smaller number of drivers is perfectly sustainable.
It just doesn't seem to scale globally very well without a continuous cash injection.