>How is that different from servers in a restaurant?

I fail to see how that is relevant. I think the closest comparison to DoorDash is ordering delivery from an Italian restaurant – not driving to the restaurant, sitting down at a table and getting table service. And yes, I think many people are aware that it is common for kitchen staff to pool tips at a restaurant, in the same way that they know the same process doesn't exist for delivery drivers.

>would you be upset if Domino's gave an earnings guarantee to their drivers?

I would have no problem with that, but if they have a button on their app that says "tip your driver" it had better all go to the driver.