Not with the Doordash model it's not. Sure you have the low paid serfs which help restaurants sidestep the various requirements applied to actual employees (e.g. transit and health insurance benefits). But you also have duplicate payment processing and customer support infrastructure, the legal staff required because your business model requires skirting or outright breaking the law, the higher rate of refunds/returns due to hawking food that's ill suited to travel (against the restaurant's wishes), drivers that now have to drive all over town to different restaurants, orders that are prioritized by the size of the attached "gratuity", etc.
The Domino's model was cheaper for the customer because it's inherently more efficient than Doordash. There were no angry restaurants suing to get off of your platform. Drivers were either making deliveries or at a specific restaurant ready to make a delivery. Customers didn't have to pay two separate merchant fees or ensure profit for two separate companies. Plus Domino's incentivized fast deliveries (there were external costs to this however), ensuring that the restaurant could efficiently utilize their delivery drivers.
Plus you're also likely underestimating the return that the vulture capitalists are demanding.
If your reduce your client's costs by $3000 and you charge $2000 to do it, everyone is happy and you can make a nice profit.
And remember the "efficiency" is relative to tons of restaurant-specific delivery drivers. It's possible.