“But if the dasher has to relay the order then wtf?”

Why would you ever think it works this way? Have you never been in a restaurant and heard the DoorDash alert from the tablets they have behind the counter?

Customer, driver and merchant all have their own app.

Customer places order, restaurant receives order and marks it as received in their system as they start preparing it, that pings a nearby driver to go pick up the order.

I guarantee if drivers had to relay the order, everyone would be scraping Mayo and picking pickles off of their burger cause drivers don’t get paid enough to sit there and tell the restaurant every single substitution you want on every item. You’re getting it how it comes, figure it out.